Water-swellable material comprising coated water-swellable polymers

ABSTRACT

This invention relates to a water-swellable material comprising water-swellable polymers that are coated with a coating agent that comprises a phase-separating elastomeric material, which allows swelling of the water-swellable polymers, without breakage of the coating. The invention also relates to a process of making specific coated water-swellable polymers using a phase-separating elastomeric material, and materials obtainable by such a process.

FIELD OF THE INVENTION

This invention relates to a water-swellable material comprisingwater-swellable polymers that are coated with a coating agent thatcomprises a phase-separating elastomeric material, which allows swellingof the water-swellable polymers, without breakage of the coating. Theinvention also relates to a process of making specific coatedwater-swellable polymers using a phase-separating elastomeric material,and materials obtainable by such a process.

BACKGROUND OF THE INVENTION

An important component of disposable absorbent articles such as diapersis an absorbent core structure comprising water-swellable polymers,typically hydrogel-forming water-swellable polymers, also referred to asabsorbent gelling material, AGM, or super-absorbent polymers, or SAP's.This polymer material ensures that large amounts of bodily fluids, e.g.,urine, can be absorbed by the article during its use and locked away,thus providing low rewet and good skin dryness.

Especially useful water-swellable polymers or SAP's are often made byinitially polymerizing unsaturated carboxylic acids or derivativesthereof, such as acrylic acid, alkali metal (e.g., sodium and/orpotassium) or ammonium salts of acrylic acid, alkyl acrylates, and thelike in the presence of relatively small amounts of di- orpoly-functional monomers such as N,N′-methylenebisacrylamide,trimethylolpropane triacrylate, ethylene glycol di(meth)acrylate, ortriallylamine. The di- or poly-functional monomer materials serve tolightly cross-link the polymer chains thereby rendering themwater-insoluble, yet water-swellable. These lightly crosslinkedabsorbent polymers contain a multiplicity of carboxylate groups attachedto the polymer backbone. It is generally believed, that the neutralizedcarboxylate groups generate an osmotic driving force for the absorptionof body fluids by the crosslinked polymer network.

In addition, the polymer particles are often treated as to form asurface cross-linked layer on the outer surface in order to improvetheir properties in particular for application in baby diapers.

Water-swellable (hydrogel-forming) polymers useful as absorbents inabsorbent members and articles such as disposable diapers need to haveadequately high sorption capacity, as well as adequately high gelstrength. Sorption capacity needs to be sufficiently high to enable theabsorbent polymer to absorb significant amounts of the aqueous bodyfluids encountered during use of the absorbent article. Together withother properties of the gel, gel strength relates to the tendency of theswollen polymer particles to resist deformation under an applied stress.The gel strength needs to be high enough in the absorbent member orarticle, so that the particles do not deform and fill the capillary voidspaces to an unacceptable degree causing so-called gel blocking. Thisgel-blocking inhibits the rate of fluid uptake or the fluiddistribution, i.e., once gel-blocking occurs, it can substantiallyimpede the distribution of fluids to relatively dry zones or regions inthe absorbent article and leakage from the absorbent article can takeplace well before the water-swellable polymer particles are fullysaturated or before the fluid can diffuse or wick past the “blocking”particles into the rest of the absorbent article. Thus, it is importantthat the water-swellable polymers (when incorporated in an absorbentstructure or article) maintain a high wet-porosity and have a highresistance against deformation thus yielding high permeability for fluidtransport through the swollen gel bed.

Absorbent polymers with relatively high permeability can be made byincreasing the level of internal crosslinking or surface crosslinking,which increases the resistance of the swollen gel against deformation byan external pressure such as the pressure caused by the wearer, but thistypically also reduces the absorbent capacity of the gel undesirably.

The inventors have found that often the surface crosslinkedwater-swellable polymer particles are constrained by thesurface-crosslinking ‘shell’ and cannot absorb and swell sufficiently,and/or that the shell is not strong enough to withstand the stresses ofswelling or the stresses associated with performance under load.

The inventors have found that the coatings or shells of thewater-swellable polymers, as used in the art, including surfacecross-linking ‘coatings’, break when the polymer swells significantly orthat the ‘coatings’ break after having been in a swollen state for aperiod of time. They also have found that, as a result thereof, thecoated and/or surface-crosslinked water-swellable polymers orsuper-absorbent material known in the art deform significantly in usethus leading to relatively low porosity and permeability of the gel bedin the wet state. They have found that this could be detrimental to theoptimum absorbency, liquid distribution or storage performance of suchpolymer materials.

Thus, the inventors have found that what is required are water-swellablematerials comprising coated water-swellable polymers that have a coatingthat can exert a force in the wet state and that does not rupture whenthe polymers swell in body liquid under typical in-use conditions. Inthe context of this invention, the inventors have found that as a goodrepresentative for body liquids such as urine, a 0.9% sodium chloride(saline) by weight in water solution, further called “0.9% saline” canbe used. Therefore, the inventors have found that it is required to havecoated water-swellable materials where the coating does notsubstantially rupture when the materials swell in 0.9% saline.

The inventors have found that it is beneficial to coat thewater-swellable material with specific elastomeric materials. However,they have found that not all elastomeric materials are suitable in everyapplication as coating agents, because some materials have a goodelongation when in a dry state, but not in a wet state.

The inventors have found that, in order to provide the above-describedproperties and benefits, the elastomeric material should bephase-separating, and typically, it should have at least two differentglass transition temperatures, e.g., it typically has at least a first,soft phase with a first glass transition temperature Tg₁ and a second,hard component with a second glass transition temperature Tg₂.

The inventors have found that when the internal core of the hydrogelpolymers swells, this specific coating with phase separating elastomericpolymers extends and remains substantially intact, i.e., withoutbreaking.

It is believed that this is due to the cohesive nature of theelastomeric material and the high elongation to break of thephase-separating material.

The inventors also have found that it is beneficial that the coatingaround the water-swellable polymers is breathable, as defined hereinbelow, and that the coating that is formed from the coating agent isbreathable.

The inventors further found that often the process of applying and/orsubsequently treating the coating agents may be important in order toimpart high elongation in the wet state.

SUMMARY OF THE INVENTION

The invention provides, in a first embodiment, a water-swellablematerial, comprising water-swellable polymers that are coated with acoating agent, which comprises an elastomeric material that isphase-separating, having at least a first phase with a first glasstransition temperature Tg₁ and a second phase with a second glasstransition temperature Tg₂, preferably the difference between Tg₁ andTg₂ being at least 30° C.

The invention also provides a process for making a water-swellablematerial that comprises coated water-swellable polymer particles, andmaterials obtainable thereby, said process comprising the steps of:

-   -   a) obtaining water-swellable polymer particles;    -   b) simultaneously with or subsequently to step a), applying a        coating agent to at least a part of said water-swellable        polymers particles, to obtain coated water-swellable polymer        particles; and optionally the step of    -   c) annealing the resulting coated water-swellable polymer        particles of step b),    -   whereby said coating agent of step b) comprises an elastomeric        phase-separating material that has at least a first phase with a        first glass transition temperature Tg₁ and a second phase with a        second glass transition temperature Tg₂, preferably the        difference between Tg₁ and Tg₂ being at least 30° C.

In general, the elastomeric phase-separating material has a Tg₁ of lessthan room temperature, e.g., less than 25° C., but it is hereinpreferred that Tg₁ is less than 20° C., or even less than 0° C. and aTg₂ is preferably more than room temperature, preferably more than 50°C., or even more than 60° C.

The elastomeric material is preferably a phase-separating blockcopolymeric material, having a weight average molecular weight of atleast 50 kDa, preferably at least 70 kDa, as can be determined by gelpermeation chromatography using a multi-angle laser light scatteringdetector, as known in the art.

The coating agent and/or said elastomeric material is preferablywet-extensible and has a wet-elongation at break (as determined by thetest method herein) of at least 400% and a tensile stress at break inthe wet state of at least 1 MPa, or even at least 5 MPa, and itpreferably has, in the wet state, a wet secant elastic modulus at 400%elongation of at least 0.25 MPa, preferably at least 0.50 MPa, morepreferably at least about 0.75 MPa, or even at least about 2 MPa, mostpreferably at least 3 MPa.

Preferably, the coating agent and/or the wet-extensible elastomericmaterial (made into a film, as set out in the test method below) has, inthe dry state, a dry secant modulus at 400% elongation (SM_(dry400%))and a wet secant modulus at 400% elongation (SM_(wet400%)), whereby theratio of SM_(wet400%) to SM_(dry400%)) is between 1.4 to 0.6.

The coating formed from the coating agent is preferably breathable,which means for the purpose of the invention that a film hereof (asdescribed in the MVTR test method set out below) has preferably amoisture vapour transmission rate of at least 800 g/m²/day, orpreferably at least 1200 g/m²/day, or even at least 1500 g/m²/day orpreferably at least 2100 g/m²/day.

The annealing step is typically done at a temperature which is at least20° C. above the highest Tg, as described herein. If the coating agentor phase-separating material has a Tm, then said annealing of the films(prepared as set out above and to be tested by the methods below) isdone at a temperature which is above the (highest) Tg and at least 20°C. below the Tm and (as close to) 20° C. above the (highest) Tg. Forexample, a wet-extensible material that has a Tm of 135° C. and ahighest Tg (of the hard segment) of 100° C., would be annealed at 115°C.

DETAILED DESCRIPTION

Water-Swellable Material

The water-swellable material of the invention is such that it swells inwater by absorbing the water; it may thereby form a gel. It may alsoabsorb other liquids and swell. Thus, when used herein,‘water-swellable’ means that the material swells at least in water, buttypically also in other liquids or solutions, preferably in water basedliquids such as 0.9% saline.

The water-swellable material of the invention comprises water-swellablepolymers that are coated with a coating agent, as described below. Thewater-swellable material may also contain water-swellable polymers thatare not coated. However, the coated water-swellable polymers arepreferably present at a level of at least 20% by weight (of thewater-swellable material), more preferably from 50% to 100% by weight oreven from 80% to 100% by weight, and most preferably between 90% and100% by weight.

The coated water-swellable polymers may be present in thewater-swellable material of the invention mixed with other components,such as fibers, (fibrous) glues, organic or inorganic filler materialsor flowing aids, process aids, anti-caking agents, odor control agents,colouring agents, coatings to impart wet stickiness, hydrophilic surfacecoatings, etc.

The coating agent is applied such that the resulting coating layer ispreferably thin; preferably the coating layer has an average caliper(thickness) between 1 micron (μm) and 100 microns, preferably from 1micron to 50 microns, more preferably from 1 micron to 20 microns oreven from 2 to 20 microns or even from 2 to 10 microns.

The coating is preferably uniform in caliper and/or shape. Preferably,the average caliper is such that the ratio of the smallest to largestcaliper is from 1:1 to 1:5, preferably from 1:1 to 1:3, or even 1:1 to1:2, or even 1:1 to 1:1.5.

The level of the coating agent is dependent on the level of the coatedpolymers, but typically, the coating agent is present at a level of 0.5%to 40% by weight of the water-swellable material, more preferably from1% to 30% by weight or even from 1% to 20% by weight or even from 2% to15% by weight.

The water-swellable material is typically obtainable by the processdescribed herein, which is such that the resulting material is solid;this includes gels, flakes, fibers, agglomerates, large blocks,granules, particles, spheres and other forms known in the art for thewater-swellable polymers described hereinafter.

Preferably, the material is in the form of particles having a massmedian particle size between up to 2 mm, or even between 50 microns and1 mm, or preferably between 100 μm and 800 μm, as can for example bemeasured by the method set out in for example EP-A-0691133.

In one embodiment of the invention the water-swellable material of theinvention is in the form of (free flowing) particles with particle sizesbetween 10 μm and 1200 μm or even between 50 μm and 800 μm and a massmedian particle size between 100 and 800 μm or preferably even to 600μm.

In addition, or in another embodiment of the invention, thewater-swellable material comprises particles that are essentiallyspherical.

In yet another preferred embodiment of the invention the water-swellablematerial of the invention has a relatively narrow range of particlesizes with the majority (e.g., at least 80% or preferably at least 90%or even at least 95%) of particles having a particle size between 50 μmand 800 μm, preferably between 100 μm and 600 μm, and more preferablybetween 200 μm and 600 μm.

The water-swellable material of the invention preferably comprises lessthan 20% by weight of water, or even less than 10% or even less than 8%or even less than 5%, or even no water. The water-content of thewater-swellable material can be determined by the EDANA test, number ERT430.1-99 (February 1999) which involves drying the water-swellablematerial at 105° Celsius for 3 hours and determining the moisturecontent by the weight loss of the water-swellable materials afterdrying.

The water-swellable material of the invention is typically made suchthat it is in the form of so-called core-shell particles, whereby thewater-swellable polymer(s) is present in the internal structure or coreand the coating agent forms a coating shell around the water-swellablepolymers, as described below in more detail.

In one preferred embodiment of the invention, the coating is anessentially continuous coating layer or shell around the water-swellablepolymer (core), and said coating layer covers the entire surface of thepolymer(s), i.e., no regions of the polymer's surface (core surface) areexposed. Hereby, it is believed that maximum tangential forces areexerted around the water-swellable polymer in the ‘core’ when thewater-swellable material swells in a liquid, as described below. Inparticular in this embodiment, the coating materials and the resultingcoatings are preferably highly water permeable such as to allow a fastpenetration/absorption of liquid into the water-swellable material (intothe core).

In another preferred embodiment of the invention, the coating shell orlayer is porous, e.g., in the form of a network comprising pores forpenetration of water, such as for example in the form of a fibrousnetwork, e.g., that is connected and circumscribing the particle asdefined herein.

In other words, it is highly preferred that the resulting coating orcoating layer or shell, formed in the process herein, is pathwiseconnected and more preferably that the coating layer is pathwiseconnected and encapsulating (completely circumscribing) thewater-swellable polymer(s) (see for example E. W. Weinstein et. al.,Mathworld—A Wolfram Web Resource for ‘encapsulation’ and ‘pathwiseconnected’).

The coating layer is preferably a pathwise connected complete surface onthe surface of the (‘core’ of the) water-swellable polymer(s). Thiscomplete surface consists of first areas where the coating agent ispresent and which are pathwise connected, e.g., like a network, and itmay comprise second areas, where no coating agent is present, being forexample micro pores, whereby said second areas are a disjoint union.Preferably, each second area, e.g., micropore, has a surface area ofless than 0.1 mm², or even less than 0.01 mm² preferably less than 8000μm², more preferably less than 2000 μm² and even more preferably lessthan 80 μm².

It is most preferred that no second areas are present, and that thecoating agent forms a complete encapsulation around the water-swellablepolymer (s).

Preferred may be that the water-swellable material comprises two or morelayers of coating agent (shells), obtainable by coating thewater-swellable polymers twice or more. This may be the same coatingagent or a different coating agent.

Especially preferred water-swellable materials made by the process ofthe invention have a high sorption capacity measured by the CylinderCentrifugation Retention Capacity, CCRC, test outlined below.

Especially preferred water-swellable materials made by the process ofthe invention have a high permeability for liquid such as can bemeasured by the SFC test disclosed in U.S. Pat. No. 5,599,335, U.S. Pat.No. 5,562,646 and U.S. Pat. No. 5,669,894 all of which are incorporatedherein by reference.

Most preferred water-swellable materials made by the process of theinvention have a high sorption capacity such as preferably measured bythe CCRC test outlined below in combination with a high permeability(SFC) and high wet porosity (increased by the use of the coating agent).

In addition, especially preferred water-swellable materials made by theprocess of the invention have a high wet porosity (i.e., this means thatonce an amount of the water-swellable material of the invention isallowed to absorb a liquid and swell, it will typically form a(hydro)gel or (hydro)gel bed, which has a certain wet porosity, inparticular compared to the uncoated water-swellable polymers, as can bemeasured by the SFC test set out herein (or with the PHL test disclosedin U.S. Pat. No. 5,562,646 which is incorporated herein by reference; ifthe water-swellable material and water-swellable polymers are to betested at different pressures than described in the test method, theweight used in this test should be adjusted accordingly).

The use of the coating agent preferably increases the wet porosity ofthe water-swellable material herein, compared to the uncoatedwater-swellable polymers; preferably this increase is at least 50% oreven at least 100%, or even at least 150%. More preferably, the wetporosity of the coated water-swellable materials herein increases underpressure such as the pressure caused by the wearer.

Water-Swellable Polymers

The water-swellable polymers herein are preferably solid, preferably inthe form of particles (which includes for example particles in the formof flakes, fibers, agglomerates); most preferably, the polymers areparticles having a mass median particle size as specified above for thewater-swellable material. The water-swellable polymers may have the massmedian particle sizes and distributions as cited above for the coatedmaterials, plus the thickness (caliper) of the coating; however, whenfor the purpose of the invention, the coating thickness is neglectable(for example being 2 to 20 microns), the water-swellable polymerstypically have a mass median particle size/distribution which is thesame as those cited above for the coated material.

As used herein, the term “water-swellable polymer” refers to a polymerwhich is substantially water-insoluble, water-swellable and preferablywater-gelling, forming a hydrogel, and which has typically a CylinderCentrifuge Retention Capacity (CCRC) as defined below of at least 10g/g. These polymers are often also referred to in the art as (super-)absorbent polymers (SAP) or absorbent gelling materials (AGM).

These polymers are typically (lightly) crosslinked polymers, preferablylightly crosslinked hydrophilic polymers. While these polymers may ingeneral be non-ionic, cationic, zwitterionic, or anionic, the preferredpolymers are cationic or anionic. Especially preferred are acidpolymers, which contain a multiplicity of acid functional groups such ascarboxylic acid groups, or their salts, preferably sodium salts.Examples of acid polymers suitable for use herein include those whichare prepared from polymerizable, acid-containing monomers, or monomerscontaining functional groups which can be converted to acid groups afterpolymerization. Such monomers include olefinically unsaturatedcarboxylic acids and anhydrides, and mixtures thereof. The acid polymerscan also comprise polymers that are not prepared from olefinicallyunsaturated monomers. Examples of such polymers also includepolysaccharide-based polymers such as carboxymethyl starch andcarboxymethyl cellulose, and poly(amino acid) based polymers such aspoly(aspartic acid). For a description of poly(amino acid) absorbentpolymers, see, for example, U.S. Pat. No. 5,247,068, issued Sep. 21,1993 to Donachy et al.

Some non-acid monomers can also be included, usually in minor amounts,in preparing the absorbent polymers herein. Such non-acid monomers caninclude, for example, monomers containing the following types offunctional groups: carboxylate or sulfonate esters, hydroxyl groups,amide-groups, amino groups, nitrile groups, quaternary ammonium saltgroups, and aryl groups (e.g., phenyl groups, such as those derived fromstyrene monomer). Other optional non-acid monomers include unsaturatedhydrocarbons such as ethylene, propylene, 1-butene, butadiene, andisoprene. These non-acid monomers are well-known materials and aredescribed in greater detail, for example, in U.S. Pat. No. 4,076,663(Masuda et al.), issued Feb. 28, 1978, and in U.S. Pat. No. 4,062,817(Westerman), issued Dec. 13, 1977.

Olefinically unsaturated carboxylic acid and anhydride monomers usefulherein include the acrylic acids typified by acrylic acid itself,methacrylic acid, α-chloroacrylic acid, α-cyanoacrylic acid,β-methylacrylic acid (crotonic acid), α-phenylacrylic acid,β-acryloxypropionic acid, sorbic acid, α-chlorosorbic acid, angelicacid, cinnamic acid, p-chlorocinnamic acid, β-stearylacrylic acid,itaconic acid, citroconic acid, mesaconic acid, glutaconic acid,aconitic acid, maleic acid, fumaric acid, tricarboxyethylene, and maleicanhydride.

Preferred water-swellable polymers contain carboxyl groups, such as theabove-described carboxylic acid/carboxylate containing groups. Thesepolymers include hydrolyzed starch-acrylonitrile graft copolymers,partially neutralized hydrolyzed starch-acrylonitrile graft copolymers,starch-acrylic acid graft copolymers, partially neutralizedstarch-acrylic acid graft copolymers, hydrolyzed vinyl acetate-acrylicester copolymers, hydrolyzed acrylonitrile or acrylamide copolymers,slightly network crosslinked polymers of any of the aforementionedcopolymers, polyacrylic acid, and slightly network crosslinked polymersof polyacrylic acid. These polymers can be used either solely or in theform of a mixture of two or more different polymers. Examples of thesepolymer materials are disclosed in U.S. Pat. No. 3,661,875, U.S. Pat.No. 4,076,663, U.S. Pat. No. 4,093,776, U.S. Pat. No. 4,666,983, andU.S. Pat. No. 4,734,478.

Most preferred polymer materials used for making the water-swellablepolymers herein are polyacrylates/acrylic acids and derivatives thereof,preferably (slightly) network crosslinked polymers partially neutralizedpolyacrylic acids and/or -starch derivatives thereof.

Preferred may be that partially neutralized polymeric acrylic acid isused in the process herein.

The water-swellable polymers useful in the present invention can beformed by any polymerization and/or crosslinking techniques. Typicalprocesses for producing these polymers are described in U.S. ReissuePatent 32,649 (Brandt et al.), issued Apr. 19, 1988, U.S. Pat. No.4,666,983 (Tsubakimoto et al.), issued May 19, 1987, and U.S. Pat. No.4,625,001 (Tsubakimoto et al.), issued Nov. 25, 1986; U.S. Pat. No.5,140,076 (Harada); U.S. Pat. No. 6,376,618 B1, U.S. Pat. No. 6,391,451and U.S. Pat. No. 6,239,230 (Mitchell); U.S. Pat. No. 6,150,469(Harada). Crosslinking can be affected during polymerization byincorporation of suitable crosslinking monomers. Alternatively, thepolymers can be crosslinked after polymerization by reaction with asuitable reactive crosslinking agent. Surface crosslinking of theinitially formed polymers is a preferred way to control to some extentthe absorbent capacity, porosity and permeability.

The water-swellable polymers may also be surface-crosslinked, prior to,simultaneously with or after the coating step of the process herein.Suitable general methods for carrying out surface crosslinking ofabsorbent polymers according to the present invention are disclosed inU.S. Pat. No. 4,541,871 (Obayashi), issued Sep. 17, 1985; published PCTapplication WO92/16565 (Stanley), published Oct. 1, 1992, published PCTapplication WO90/08789 (Tai), published Aug. 9, 1990; published PCTapplication WO93/05080 (Stanley), published Mar. 18, 1993; U.S. Pat. No.4,824,901 (Alexander), issued Apr. 25, 1989; U.S. Pat. No. 4,789,861(Johnson), issued Jan. 17, 1989; U.S. Pat. No. 4,587,308 (Makita),issued May 6, 1986; U.S. Pat. No. 4,734,478 (Tsubakimoto), issued Mar.29, 1988; U.S. Pat. No. 5,164,459 (Kimura et al.), issued Nov. 17, 1992;published German patent application 4,020,780 (Dahmen), published Aug.29, 1991; U.S. Pat. No. 5,140,076 (Harada); U.S. Pat. No. 6,376,618 B1,U.S. Pat. No. 6,391,451 and U.S. Pat. No. 6,239,230 (Mitchell); U.S.Pat. No. 6,150,469 (Harada); and published European patent application509,708 (Gartner), published Oct. 21, 1992.

Most preferably, the water-swellable polymers comprise from about 50% to95% (mol percentage), preferably about 75 mol % neutralized, (slightly)crosslinked, polyacrylic acid (i.e., poly (sodium acrylate/acrylicacid)). Crosslinking renders the polymer substantially water-insolubleand, in part, determines the absorptive capacity and extractable polymercontent characteristics of the absorbent polymers. Processes forcrosslinking these polymers and typical bulk crosslinking agents aredescribed in greater detail in U.S. Pat. No. 4,076,663.

While the water-swellable polymer is preferably of one type (i.e.,homogeneous), mixtures of water-swellable polymers can also be used inthe present invention. For example, mixtures of starch-acrylic acidgraft copolymers and slightly network crosslinked polymers ofpolyacrylic acid can be used in the present invention. Mixtures of(coated) polymers with different physical properties, and optionallyalso different chemical properties, could also be used, e.g., differentmean particle size, absorbent capacity, absorbent speed, SFC value, suchas for example disclosed in U.S. Pat. No. 5,714,156 which isincorporated herein by reference.

The water-swellable polymers herein preferably have, prior to coating, aCylinder Centrifuge Retention Capacity (CCRC) of at least 30 g/g,preferably at least 40 g/g, more preferably at least 50 g/g.

The water-swellable polymers preferably have a low amount ofextractables, preferably less than 15% (by weight of the polymers), morepreferably less than 10% and most preferably less than 5% ofextractables, or even less than 3% (values of 1 hour test). Theextractables and levels thereof and determination thereof is furtherdescribed in, for example, U.S. Pat. No. 5,599,335; U.S. Pat. No.5,562,646 or U.S. Pat. No. 5,669,894.

Coating Agent and Elastomeric Phase-Separating Material Thereof

The coating agent herein comprises at least an elastomeric material thatis phase-separating.

‘Elastomeric’ when used herein means that the material will exhibitstress induced deformation that is partially or completely reversed uponremoval of the stress. The preferred tensile properties of elastomericmaterials (formed into films) may be measured according to the testmethod defined herein to determine the wet and dry elongation to breakand secant modulus at 400% elongation.

‘Phase-separating’ elastomeric material, when used herein, means that afilm of the elastomeric material (i.e., prior to use in the coatingagent and application to the water-swellable polymers) has at least twodistinct spacial phases which are distinct and separated from oneanother, due to their thermodynamic incompatibility. The incompatiblephases are comprised of aggregates of only one type of repeat unit orsegment of the elastomeric material. This can for example occur when theelastomeric material is a block (or segmented) copolymer, or a blend oftwo immiscible polymers. The phenomenon of phase separation is forexample described in: Thermoplastic Elastomers: A Comprehensive Review,eds. Legge, N. R., Holden, G., Schroeder, H. E., 1987, Chapter 2.

Typically, the phase separation occurs in a block copolymer, whereby thesegment or block of the copolymer that has a Tg below room temperature(i.e., below 25° C.) is said to be the soft segment or soft block andthe segment or block of the copolymer that has a Tg above roomtemperature is said to be the hard segment or hard block.

The Tg's, as referred to herein, may be measured by DifferentialScanning Calorimetry (DSC) to measure the change in specific heat that amaterial undergoes upon heating. The DSC measures the energy required tomaintain the temperature of a sample to be the same as the temperatureof the inert reference material (e.g., Indium). A Tg is determined fromthe midpoint of the endothermic change in the slope of the baseline. TheTg values are reported from the second heating cycle so that anyresidual solvent in the sample is removed.

In addition, the phase separation can also be visualized by electronmicroscopy particularly if one phase can be stained preferentially. Alsoatomic force microscopy has been described as a particularly usefultechnique to characterize the morphology (phase-separating behavior) ofthe preferred thermoplastic polyurethanes, described herein after.

The elastomeric material herein comprises at least two phases withdifferent glass transition temperatures (Tg); it comprises at least afirst phase with a Tg₁, which is lower than the Tg₂ of a second phase,the difference being at least 30° C.

Preferably, the elastomeric material has a first (soft) phase with a Tg₁which is less than 25° C., preferably less than 20° C., more preferablyless than 0° C., or even less than −20° C., and a second (hard) phasewith a Tg₂ of at least 50° C. or even at least 55° C., but morepreferably more than 60° C. or even more than 70° C., or in certainembodiments, more than 100° C., provided the temperature differencebetween Tg₁ and Tg₂ is at least 30° C., preferably at least 50° C. oreven at least 60° C., or in certain embodiments at least 90° C.

It should be understood that, for the purpose of the invention, theelastomeric material itself (i.e., before incorporation into the coatingagent or before formation into the coating on the water-swellablepolymers) has the herein specified properties, but that that typically,the elastomeric material maintains these properties once in the coatingagent and/or in the coating, and that the resulting (film of the)coating should thus preferably have the same properties.

Typically, the elastomeric material and the coating agent need to beelastomeric in the wet state. Hence, the coating agent and/or theelastomeric material has (have) a wet-elongation at break of at least400%, as determined by the test method described herein below (wherein awet film of the elastomeric material or coating agent is submitted tospecific conditions, in order to measure the wet-elongation at break;the elastomeric material is therefore thus a material that can be formedinto a film, i.e., film-forming).

Preferably, the elastomeric material has a wet elongation at break of atleast 400%, or even at least 500% or even at least 800% or even at least1000%.

It should be understood for the purpose of the invention that a film orcoating of the elastomeric material and the coating agent typicallyextend (in the wet state) their surface area, without (substantially)expanding in volume by liquid absorption. The elastomeric material andthe coating agent are thus typically substantially non-water-swelling,as for example may be determined by the method set out herein below.This means in practice that the coating agent and/or the elastomericmaterial have preferably a water-swelling capacity of less than 1 g/g,or even less than 0.5 g/g, or even less than 0.2 g/g or even less than0.1 g/g, as may be determined by the method, as set out below.

The inventors have found that (films of the) elastomeric materials withhigh moisture vapor transmission rates (at least 2100 g/m²/day asdescribed by the method herein) have higher water or saline absorptionthan those with lower MVTR, however the water or saline absorption doesnot negatively affect the wet tensile properties of resulting coating.

The elastomeric material (and preferably the coating agent as a whole)has a tensile stress at break in the wet state of at least 1 MPa, oreven at least 3 MPa and more preferably at least 5 MPa, or even at least8 MPa. This can be determined by the test method, described below.

Particularly preferred elastomeric materials and/or coating agentsherein are materials that have a wet secant elastic modulus at 400%elongation (SM_(wet400%)) of at least 0.25 MPa, preferably at leastabout 0.50 MPa, more preferably at least about 0.75 or even at least 2.0MPa, and most preferably of at least about 3.0 MPa.

Preferred elastomeric materials or coating agents herein have a ratio of[wet secant elastic modulus at 400% elongation (SM_(wet400%))] to [drysecant elastic modulus at 400% elongation (SM_(dry400%))] of 1.4 orless, preferably 1.2 or less or even 1.0 or less, and it may bepreferred that this ratio is at least 0.6, or even at least 0.7.

Preferably, the coating agent is present in the form of a coating thathas a shell tension, which is defined as the (Theoretical equivalentshell caliper)×(Average wet secant elastic modulus at 400% elongation),of 2 to 20 N/m, or preferably 3 to 10 N/m, or more preferably 3 to 5N/m.

The coating agent is preferably such that the resulting coating on thewater-swellable polymers herein is water-permeable, but notwater-soluble and, preferably not water-dispersible. The waterpermeability of the coating should be high enough such that the coatedwater-swellable material has a sufficiently high free swell rate asdefined herein, preferably a free swell rate (FSR) of at least 0.05g/g/sec, preferably at least 0.1 g/g/sec, and more preferably at least0.2 g/g/sec.

The coating agent and/or the elastomeric material are preferablymoderately or highly breathable, so that moisture vapour can pass.Preferably, the coating agent and/or elastomeric material (tested in theform of a film of a specific caliper, as described herein) is at leastmoderately breathable with a moisture vapour transmission rate (MVTR) of800 or preferably 1200 to (inclusive) 1400 g/m²/day, preferablybreathable with a MVTR of at least 1500 g/m²/day, up to 2000 g/m²/day(inclusive), and even more preferably that the coating agent or materialis highly breathable with a MVTR of 2100 g/m²/day or more.

The elastomeric material may be a mixture of two or more differentpolymers that each has a different Tg, and which form a phase-separatingmixture.

Preferred phase-separating elastomeric materials comprise a mixture ofat least a (co)polymer selected of the following group A and a(co)polymer selected of the following group B:

A: poly ethylene (co) polymers, polypropylene (co) polymers,polybutylene (co) polymers, polyisoprene (co) polymers, polybutadiene(co) polymers, polyethylene-co-polypropylene,polyethylene-co-polybutylene, polyethylethylene-co-polypropylene,polyether (co) polymers, polyester (co) polymers; which all mayoptionally be grafted and/or be partially modified with chemicalsubstituents (e.g., hydroxyl groups or carboxylates);

B: polyvinyl (co) polymers (e.g., styrene, vinylacetate,vinylformamide), polyurethanes (co) polymers, polyester (co) polymers,polyamide (co) polymers, polydimethylsiloxanes, proteins; which all mayoptionally be grafted and/or be partially modified with chemicalsubstituents (e.g., hydroxyl groups or carboxylates).

More preferably, the elastomeric material comprises one or morephase-separating block copolymer (s), whereby each of the blockcopolymers has two or more Tg's. Especially preferred phase-separatingelastomeric materials herein comprise one or more phase-separating blockcopolymer, having a weight average molecular weight Mw of at least 50kDa, preferably at least 70 kDa.

Such a block copolymer has at least a first polymerized homopolymersegment (block) and a second polymerized homopolymer segment (block),polymerized with one another, whereby preferably the first (soft)segment has a Tg₁ of less than 25° C. or even less than 20° C., or evenless than 0° C., and the second (hard) segment has a Tg₂ of at least 50°C., or of 55° C. or more, preferably 60° C. or more or even 70° C. ormore.

The total weight average molecular weight of the hard second segments(with a Tg of at least 50° C.), is preferably at least 28 kDa, or evenat least 45 kDa.

The preferred weight average molecular weight of a first (soft) segmentis at least 500 Da, preferably at least 1000 Da or even at least 2000Da, but preferably less than 8000 Da, preferably less than 5000 Da.

However, the total of the total of the first (soft) segments istypically 20% to 95% by weight of the total block copolymer, or evenfrom 20% to 70% or more preferably from 30% to 60% or even from 30% to40% by weight. Furthermore, when the total weight level of soft segmentsis more than 70%, it is even more preferred that an individual softsegment has a weight average molecular weight of less than 5000 Da.

It may be preferred that the block copolymer comprises a mixture ofdifferent soft segments and/or a mixture of different hard segments, forexample a mixture of different soft segments that each have a differentTg, but all less than 25° C. or even less than 20° C., or even less than0° C., or for example a mixture of hard segments, each having adifferent Tg, but all greater than 50° C.

The precise weight level (in the block copolymer) of the first segmentsthat have a Tg of less than 25° C., or even less than 20° C. or evenless than 0° C., will depend on the required tensile strength of theresulting coating, e.g., by decreasing the weight level of the firstsegments in the block copolymer, the tensile strength may increase.However, when the weight percentage of the first segments is too low,the MVTR may be lower than desirable.

The block copolymers useful herein are preferably block copolymers thathave intermolecular H-bonding.

The block copolymers useful herein are preferably selected from:polyurethane (co) polyethers, polyurethane (co)polyesters,polyurethane/urea- co-polyethers or -co (poly) esters, polystyrene blockcopolymers, hydrogenated polystyrene block copolymers, polyester (co)polyethers, polyester (co) polyethers, polyamide- co-polyethers or -co(poly) esters, polyoxyethylene-co-polyepichlorohydrin.

Preferred are polyurethane-co-poly(ethylene glycol),polyurethane-co-poly(tetramethylene glycol), andpolyurethane-co-poly(propylene glycol) and mixtures thereof.

The polyurethane (hard) segments are preferably derived from apolymerisation reaction of a diisocyanate with a diol, such as forexample butane diol, or cyclohexane diol, or preferably from apolymerisation reaction of an aromatic diisocyanate and an aliphaticdiol such as ethylene glycol, butane diol, propane diol, or mixturesthereof.

A preferred diisocyanate used to form the polyurethane segments of theblock copolymers herein is methylene bis (phenyl isocyanate).

The hard segments are reacted with for example macrodiols to form thepreferred phase-separated block copolymers herein.

Preferred may be that the elastomeric phase-separating materialcomprises a block copolymer with poly (tetramethylene glycol), or morepreferably poly(ethylene glycol) segments (as first (soft) segments witha Tg of less than 20° C.), because poly(ethylene glycol) provides ahigher breathability of the resulting coating. Also, the molecularweight percentage (by weight of the total block copolymer; as discussedabove) of these first (soft) segments can be selected to provide therequired breathability, e.g., a higher percentage of these segments willprovide a more breathable coating.

Preferred phase-separating block copolymers are Vector 4211, Vector4111, Septon 2063, Septon 2007, Estane 58245, Estane 4988, Estane 4986,Estane T5410, Irogran PS370-201, Irogran VP 654/5, Pellethane 2103-70A,Elastollan LP 9109. Estane is a trade name of Noveon Inc., 9911Brecksville Road, Cleveland, Ohio 44141-3247, USA. Vector is a tradename of Dexco Polymers, 12012 Wickchester Lane, Houston, Tex. 77079,USA, Septon is a trade name of the Septon Company of America, A KurarayGroup Company, 11414 Choate Road, Pasadena, Tex. 77507, USA, Irogran isa trade name of Huntsman Polyurethanes, 52 Kendall Pond Road, Derry,N.H. 03038, USA, Pellethane is a trade name of the Dow Chemical Company,2040 Dow Center, Midland, Mich. 48674, USA and Elastollan is a tradename of BASF, 1609 Biddle Avenue, Wyandotte, Mich. 48192.

If may be preferred that the coating agent herein comprises fillers toreduce tack such as the commercially available resin Estane 58245-047P,available from Noveon Inc., 9911 Brecksville Road, Cleveland, Ohio44141-3247, USA; or the commercially available films Duraflex PT1700S,Duraflex PT1710S, Duraflex U073, Duraflex X2075, available fromDeerfield Urethane, P.O. Box 186, South Deerfield, Mass. 01373.

Preferred polymeric elastomeric materials for use in the coating agentherein are strain hardening and/or strain crystallizing. StrainHardening occurs after the rubbery plateau and is the rapid increase instress with increasing strain. Strain hardening can introduceorientation in the film producing greater resistance to extension in thedirection of drawing.

While there are some elastomeric polymers that are strain crystallizing,this property can also be imparted by the addition or blending ofadditional materials into the coating agent or polymer, such as organicor inorganic fillers. Nonlimiting examples of inorganic fillers includevarious water-insoluble salts, and other (preferably nanoparticulate)materials such as for example chemically modified silica, also calledactive or semi-active silica that are for example available as fillersfor synthetic rubbers. Examples for such fillers are UltraSil VN3,UltraSil VN3P, UltraSil VN2P, and UltraSil 7000GR available from DegussaA G, Weiβfrauenstraβe 9, D-60287 Frankfurt am Main, Germany.

Preferred fillers are organic or inorganic compounds which are useful asflow agents in the processes described herein, and which typicallyreduce the stickiness of the coated water-swellable materials or thewater-swellable polymers to be coated. Examples of such flow aids aresemi-active or hydrophobic silica, urea formaldehyde, (sodium)silicates, diatomaceous earth and clays.

The coating agent and/or the elastomeric material are preferablyhydrophilic and in particular surface hydrophilic. The surfacehydrophilicity may be determined by methods known to those skilled inthe art. In a preferred execution, the hydrophilic coating agents orelastomeric materials are materials that are wetted by the liquid thatis to be absorbed (0.9% saline; urine). They may be characterized by acontact angle that is less than 90 degrees. Contact angles can forexample be measured with the Video-based contact angle measurementdevice, Krüss G10-G1041, available from Kruess, Germany or by othermethods known in the art.

It may also be preferred that the resulting water-swellable material ishydrophilic. The hydrophilicity of water-swellable materials may bemeasured as described in co-pending application EP03014926.4

If the elastomeric material or the coating agent itself is nothydrophilic, the coating agent can be made hydrophilic for example bytreating it with surfactants, plasma coating, plasma polymerization, orother hydrophilic surface treatments as known to those skilled in theart.

Preferred compounds to be added to make the hydrophilic coating agent,or subsequently added to the resulting coated water-swellable polymersare for example: N-(2-Acetamido)-2-aminoethansulfonic-acid,N-(2-Acetamido)-imino-di-acetic-acid, N-acetyl-glycine, β-Alanine,Aluminum-hydroxy-acetate, N-Amidino-glycine,2-Amino-ethyl-hydrogenphosphate, 2-Amino-ethyl-hydrogensulfate,Amino-methan-sulfonic acid, Maleinic acid, Arginine, Asparaginic acid,Butane-diacid, Bis(1-aminoguanidinium)-sulfate, 2-Oxo-propionic acid,Tri-Calcium-dicitrate, Calcium gluconate, Calcium saccharate,Calcium-Titriplex®, Carnitin, Cellobiose, Citrullin, Creatine,Dimethylaminoacetic acid, THAM-1,2-disulfonic-acid, Ethylendiammoniumsulfate, Fructose, Fumaric acid, Galactose, Glucosamine, Gluconic-acid,Glutamine, 2-Amino-glutaric-acid, Glutaric acid, Glycine, Glycylglycine,Iminodiacetic acid, Magnesium glycerophosphate, Oxalic acid,Tetrahydroxy-adipinic acid, Taurin, N-Methyl-taurin,Tris-(hydroxymethyl)-aminomethane,N-(Tris-(hydroxymethyl)-methyl)-2-aminoethansulfonic acid.

Alternatively, the coating agent can be made hydrophilic with ahydrophilicity boosting composition comprising a hydrophilicity-boostingamount of nanoparticles. By hydrophilicity boosting amount, it isintended that an amount of nanoparticles be present in thehydrophilicity boosting compositions, which are sufficient to make asubstrate to which it is applied more hydrophilic. Such amounts arereadily ascertained by one of ordinary skill in the art; it is based onmany factors, including but not limited to, the substrate used, thenanoparticles used, the desired hydrophilicity of the resultingwater-swellable material.

Nanoparticles are particles that have a primary particle size, that isdiameter, which is in the order of magnitude of nanometers. That is,nanoparticles have a particle size ranging from about 1 to about 750nanometers. Nanoparticles with particle sizes ranging from about 2 nm toabout 750 nm can be economically produced. Non-limiting examples ofparticle size distributions of the nanoparticles are those that fallwithin the range from about 2 nm to less than about 750 nm,alternatively from about 2 nm to less than about 200 nm, andalternatively from about 2 nm to less than about 150 nm.

The particle size of the nanoparticles is the largest diameter of ananoparticle and may be measured by any methods known to those skilledin the art.

The mean particle size of various types of nanoparticles (as determinedfrom the particle size distribution) may differ from the individualparticle size of the nanoparticles particles. For example, a layeredsynthetic silicate can have a mean particle size of about 25 nanometerswhile its particle size distribution can generally vary between about 10nm to about 40 nm. (It should be understood that the particle sizes thatare described herein are for particles when they are dispersed in anaqueous medium and the mean particle size is based on the mean of theparticle number distribution. Non-limiting examples of nanoparticles caninclude crystalline or amorphous particles with a particle size fromabout 2 to about 750 nanometers. Boehmite alumina can have an averageparticle size distribution from 2 to 750 nm.

The hydrophilicity boosting composition may consist of thenanoparticles, and then the nanoparticles are directly added to thesurface-treatment agent or to the process, e.g., in step b).

Alternatively, the nanoparticles are present in a composition with othercarrier ingredients, e.g., solvents or disperent liquids; in onepreferred embodiment the nanoparticles are applied in step b) as adispersion in a liquid. If the hydrophilicity boosting composition doesnot consist of the nanoparticles, but comprises other ingredients, thenit is preferred that the nanoparticles are present in the hydrophilicityboosting compositions at levels of from about 0.0001% to about 50%,preferably from about 0.001% to about 20% or even to 15%, and morepreferably from about 0.001% to about 10%, by weight of the composition.

Either organic or inorganic nanoparticles may be used in thehydrophilicity boosting composition; inorganic nanoparticles arepreferred. Inorganic nanoparticles generally exist as oxides, silicates,carbonates and hydroxides. Some layered clay minerals and inorganicmetal oxides can be examples of nanoparticles. The layered clay mineralssuitable for use in the present invention include those in thegeological classes of the smectites, the kaolins, the illites, thechlorites, the attapulgites and the mixed layer clays. Typical examplesof specific clays belonging to these classes are the smectices, kaolins,illites, chlorites, attapulgites and mixed layer clays. Smectites, forexample, include montmorillonite, bentonite, pyrophyllite, hectorite,saponite, sauconite, nontronite, talc, beidellite, volchonskoite.Kaolins include kaolinite, dickite, nacrite, anfigorite, anauxite,halloysite, indellite and chrysotile. Illites include bravaisite,muscovite, paragonite, phlogopite and biotite, and vermiculite.Chlorites include corrensite, penninite, donbassite, sudoite, pennineand clinochlore. Attapulgites include sepiolite and polygorskyte. Mixedlayer clays include allevardite and vermiculitebiotite. Variants andisomorphic substitutions of these layered clay minerals offer uniqueapplications.

Layered clay minerals may be either naturally occurring or synthetic. Anexample of one non-limiting embodiment of the coating composition usesnatural or synthetic hectorites, montmorillonites and bentonites.Another embodiment uses the hectorites clays commercially available, andtypical sources of commercial hectorites are the LAPONITEs™ fromSouthern Clay Products, Inc., U.S.A; VEEGUM Pro and VEEGUM F from R. T.Vanderbilt, U.S.A.; and the Barasyms, Macaloids and Propaloids fromBaroid Division, National Read Comp., U.S.A.

In one preferred embodiment of the present invention the nanoparticlescomprise a synthetic hectorite a lithium magnesium silicate. One suchsuitable lithium magnesium silicate is LAPONITE™, which has the formula:[Mg_(w)Li_(x)Si₈O₂₀OH_(4-y)F_(y)]^(z−)wherein w=3 to 6, x=0 to 3, y=0 to 4, z=12−2w−x, and the overallnegative lattice charge is balanced by counter-ions; and wherein thecounter-ions are selected from the group consisting of selected Na⁺, K⁺,NH₄ ⁺, Cs⁺, Li⁺, Mg⁺⁺, Ca⁺⁺, Ba⁺⁺, N(CH₃)₄ ⁺ and mixtures thereof. (Ifthe LAPONITE™ is “modified” with a cationic organic compound, then the“counter-ion” could be viewed as being any cationic organic group (R⁺).)

Other suitable synthetic hectorites include, but are not limited toisomorphous substitutions of LAPONITE™, such as, LAPONITE B™, LAPONITES™, LAPONITE XLS™, LAPONITE RD™, LAPONITE XLG™, and LAPONITE RDS™.

The nanoparticles may also be other inorganic materials, includinginorganic oxides such as, but not limited to, titanium oxide silica,zirconium oxide, aluminum oxide, magnesium oxide and combinationsthereof. Other suitable inorganic oxides include various other inorganicoxides of alumina and silica.

In one preferred embodiment of the present invention the nanoparticlescomprise a Boehmite alumina ([Al(O)(OH)]_(n)) which is a waterdispersible, inorganic metal oxide that can be prepared to have avariety of particle sizes or range of particle sizes, including a meanparticle size distribution from about 2 nm to less than or equal toabout 750 nm. For example, a boehmite alumina nanoparticle with a meanparticle size distribution of around 25 nm under the trade name DisperalP2™ and a nanoparticle with a mean particle size distribution of around140 nm under the trade name of Dispal™ 14N4-25 are available from NorthAmerican Sasol, Inc.

In one preferred embodiment of the present invention the nanoparticlesare selected from the group consisting of titanium dioxide, Boehmitealumina, sodium magnesium lithium fluorosilicates and combinationsthereof.

Use of mixtures of nanoparticles in the hydrophilicity boostingcompositions is also within the scope of the present invention.

Optionally, in addition to or in place of water, the carrier cancomprise a low molecular weight organic solvent. Preferably, the solventis highly soluble in water, e.g., ethanol, methanol, acetone, methylethyl ketone, dimethylformamide, ethylene glycol, propanol, isopropanol,and the like, and mixtures thereof. Low molecular weight alcohols canreduce the surface tension of the nanoparticle dispersion to improvewettability of the substrate. This is particularly helpful when thesubstrate is hydrophobic. Low molecular weight alcohols can also helpthe treated substrate to dry faster. The optional water-soluble lowmolecular weight solvent can be used at any suitable level. The carriercan comprise any suitable amount of the composition, including but notlimited to from about 10% to about 99%, alternatively from about 30% toabout 95%, by weight of the coating composition.

The hydrophilicity boosting composition may also comprise organic, e.g.,latex nanoparticles, so-called nanolatexes. A “nanolatex”, as usedherein, is a latex with a particle size less than or equal to about 750nm. A “latex” is a dispersion of water-insoluble polymer particles thatare usually spherical in shape. Nanolatexes may be formed by emulsionpolymerization. “Emulsion polymerization” is a process in which monomersof the latex are dispersed in water using a surfactant to form a stableemulsion followed by polymerization. Particles are typically producedwhich can range in size from about 2 to about 600 nm. When thenanolatexes are elastomeric material, e.g., film-forming elastomericpolymers, then they are considered coating agents for the purpose of theinvention, and not (part of) a hydrophilicity boosting composition.

Surfactants are especially useful as additional ingredient of thecoating agent herein, or as additional ingredients in the process stepa) or b) herein, e.g., as wetting agents to facilitate the dispersion ofthe coating agent onto the substrate. Surfactants are preferablyincluded when the coating composition is used to treat a hydrophobicsubstrate.

Suitable surfactants can be selected from the group including anionicsurfactants, cationic surfactants, nonionic surfactants, amphotericsurfactants, ampholytic surfactants, zwitterionic surfactants andmixtures thereof. Nonlimiting examples of surfactants useful in thecompositions of the present invention are disclosed in McCutcheon's,Detergents and Emulsifiers, North American edition (1986), published byAllured Publishing Corporation; McCutcheon's, Functional Materials,North American Edition (1992); U.S. Pat. Nos. 5,707,950 and 5,576,282;and U.S. Pat. No. 3,929,678, to Laughlin et al., issued Dec. 30, 1975.

When a surfactant is used in the coating composition, it may be added atan effective amount to provide or facilitate application of the coatingcomposition. Surfactant, when present, is typically employed incompositions at levels of from about 0.0001% to about 60%, preferablyfrom about 0.001% to about 35%, and more preferably from about 0.001% toabout 25%, by weight of the composition.

Nonlimiting examples of surfactants, including preferred nonionicsurfactants, useful herein typically at levels from about 0.001% toabout 60%, by weight, include nonionic and amphoteric surfactants suchas the C₁₂-C₁₈ alkyl ethoxylates (“AE”) including the so-called narrowpeaked alkyl ethoxylates and C₆-C₁₂ alkyl phenol alkoxylates (especiallyethoxylates and mixed ethoxy/propoxy), C₁₂-C₈ betaines and sulfobetaines(“sultaines”), C₁₀-C₁₈ amine oxides, and the like. Another class ofuseful surfactants is silicone surfactants and/or silicones. They can beused alone and/or alternatively in combination with the alkyl ethoxylatesurfactants described herein. Nonlimiting examples of siliconesurfactants are the polyalkylene oxide polysiloxanes having a dimethylpolysiloxane hydrophobic moiety and one or more hydrophilic polyalkyleneside chains, and having the general formula:R¹—(CH₃)₂SiO—[(CH₃)₂SiO]_(a)—[(CH₃)(R¹)SiO]_(b)—Si(CH₃)₂—R¹wherein a+b are from about 1 to about 50, and each R¹ is the same ordifferent and is selected from the group consisting of methyl and apoly(ethyleneoxide/propyleneoxide) copolymer group having the generalformula: —(CH₂)_(n)O(C₂H₄O)_(c)(C₃H₆O)_(d)R² ,wherein n is 3 or 4; totalc (for all polyalkyleneoxy side groups) has a value of from 1 to about100, alternatively from about 6 to about 100; total d is from 0 to about14; alternatively d is 0; total c+d has a value of from about 5 to about150, alternatively from about 9 to about 100 and each R² is the same ordifferent and is selected from the group consisting of hydrogen, analkyl having 1 to 4 carbon atoms, and an acetyl group, alternativelyhydrogen and methyl group. Each polyalkylene oxide polysiloxane has atleast one R¹ group being a poly(ethyleneoxide/propyleneoxide) copolymergroup. Silicone superwetting agents are available from Dow Corning assilicone glycol copolymers (e.g., Q2-5211 and Q2-5212).

It is also within the scope of the present invention to use a mixture ofsurfactants.

The coating agent may be applied in fluid form, e.g., as a melt (orso-called hotmelt), solution or dispersion. Thus, the coating agent mayalso comprise a solvent or dispersing liquid, such as water, THF(tetrahydrofuran), methylethyl ketone, dimethylformamide, toluene,dichloromethane, cyclohexane or other solvents or dispersing liquidsthat are able to dissolve or disperse the elastomeric material (e.g.,elastomeric polymer) and subsequently can be evaporated such as to forma (dry) coating shell or layer.

Preferably, the coating agent comprises from 0% to 95% by weight of adispersing liquid or solvent, such as water. Preferred is that thecoating agent comprises at least 5% by weight (of the coating agent) ofthe elastomeric material, more preferably from 10% to 80% or even from20% to 70%, the remaining percentage being said liquid and/orfillers/hydrophilicity aids, spreading aids, etc., as described herein.

The inventors also found that the process of applying and subsequentlytreating the coating agent may be important in order to impart highelongation in the wet state.

While some elastomeric materials may already have high wet elongationper se, it may be useful to apply an annealing step, as describedherein, to the material.

In addition to providing the right mechanical properties in the wetstate as it is outlined above, preferred coating agents of the inventionpreferably also have other desired properties such as high resistanceagainst mechanical abrasion in order to survive processing intoabsorbent articles or structures, without significant deterioration oftheir properties. They also are preferably colorless, or white andopaque and may in addition contain other materials such for example tocontrol odor, release perfumes, and the like.

Process of the Invention for Making the Solid Water-Swellable Material

The process of the invention comprising the steps of:

-   -   a) obtaining water-swellable polymer particles;    -   b) simultaneously with or subsequently to step a), applying a        coating agent to at least a part of said water-swellable        polymers particles; and optionally the step of    -   c) annealing the resulting coated water-swellable polymer        particles of step b), to obtain the water-swellable material        herein,    -   whereby said coating agent of step b) comprises an elastomeric        phase-separating material that has at least a first phase with a        first glass transition temperature Tg₁ and a second phase with a        second glass transition temperature Tg₂, preferably the        difference between Tg₁ and Tg₂ being at least 30° C.

In step a) ‘obtaining’ the water-swellable polymer particles, asdescribed herein above, includes using commercially availablewater-swellable polymer particles, or forming the water-swellablepolymer particles by any known process from precursors.

The coating step b) may be done by any known method, for example bymixing or dispersing the water-swellable polymers (or precursorsthereto) in the coating agent or (hot) melt or solution or dispersionthereof; by spraying the coating agent, or said (hot) melt, solution ordispersion thereof onto the polymers; by introducing the coating agent,or melt, dispersion or solution thereof, and the water-swellablepolymers (or precursors thereto) in a fluidised bed or Wurster coater;by agglomerating the coating agent, or melt, solution or dispersionthereof, and the water-swellable polymers (or precursors thereof); bydip-coating the (particulate) water-swellable polymers in the coatingagent, melt, dispersion or solution thereof. Other suitable mixersinclude for example twin drum mixers, so called “Zig-Zag” mixers,plough-share mixers, such as Lödige mixers, cone screw mixers, orperpendicularly cylindrical mixers having coaxially rotating blades.Examples of preferred coating processes are for example described inU.S. Pat. No. 5,840,329 and U.S. Pat. No. 6,387,495.

In an alternative embodiment of the invention, the coating step b) maybe done by applying the coating agent in the form of a foam, preferablyin the form of an open-cell foam, leading to a porous coating. In yet analternative embodiment the coating step may be done by forming a fibrousnetwork on the surface of the water-swellable material such as forexample by applying the coating agent in the form of meltblownmicrofibers, such that an essentially connected coating is formed (asdescribed herein).

To apply the coating agent, it may also comprise solvents such as waterand/or organic, optionally water-miscible, solvents. Suitable organicsolvents are, for example, aliphatic and aromatic hydrocarbons,alcohols, ethers, esters, amides and ketones. Suitable water-misciblesolvents are, for example, aliphatic alcohols, polyhydric alcohols,ethers, amides and ketones.

If the coating agent is in the form of a solution or dispersion, it maybe further preferred to add processing aids, subsequently or prior tothe coating step b), e.g., in order to aid a good film formation of thecoating layer.

In the optional step c), the resulting coated water-swellable polymersare annealed. The optional annealing step c) typically involves a stepresulting in a further strengthened or more continuous or morecompletely connected coating and it may eliminate defects.

Typically, the annealing step) involves a heat treatment of theresulting coated water-swellable polymers; it may be done by for exampleradiation heating, oven heating, convection heating, azeotropic heating,and it may for example take place in conventional equipment used fordrying, such as fluidized bed driers. Preferred may be that a vacuum isapplied as well or that the annealing is done under an inert gas (toavoid oxidation).

Preferably, the annealing step involves heating the coatedwater-swellable polymers at a temperature which is above the highest Tgof the coating agent or the elastomeric phase-separating materialthereof, preferably to a temperature which is at least 20° C. above saidhighest Tg.

For example, the highest Tg is typically at least 50° C. and theannealing temperature is at least 70° C., or even at least 100° C. oreven at least 140° C., and up to 200° C. or even up to 250° C.

If the material has a melting temperature Tm, then the annealing step isat least 20° C. below the Tm and if possible and preferably at least 20°C. or even at least 50° C. above the highest Tg.

The annealing step may be done for, for example, at least 5 minutes, oreven for at least 10 minutes or even for at least 15 minutes, or even atleast 30 minutes or even at least 1 hour or even at least 2 hours.

This heat-treatment may be done once, or it may be repeated, for examplethe heat treatment may be repeated with different temperatures, forexample first at a lower temperature, for example from 70° C. or 80° C.,to 100° C., as described above, for example for at least 30 minutes oreven 1 hour, up to 12 hours, and subsequently at a higher temperature,for example from 120° C. to 140° C., for at least 10 minutes.

Typically, the temperature and time are adjusted in order to allow goodcoating (film) formation and good phase-separation, such as to formmechanically strong coatings (films).

During the annealing step, the coated water-swellable polymers may alsobe dried at the same time. Alternatively, a separate drying step maytake place.

The resulting water-swellable material is preferably solid and thus, ifthe water-swellable polymers of step a) or the resulting coated polymersof step b) are not solid, a subsequent process step is required tosolidify the resulting coated polymers of step b), e.g., a so-calledsolidifying or preferably particle forming step, as known in the art.This may preferably be done prior to, or simultaneously with step c).

The solidifying step includes for example drying the water-swellablepolymers and/or the coated polymers of step b) (e.g., if the step binvolve a dispersion or solution of any of the ingredients) byincreasing the temperature and/or applying a vacuum, as describedherein. This may be done simultaneously with, or occur automaticallywith the annealing step c). The solidifying step may also include acooling step, if for example a melt is used.

Subsequently, any known particle forming process may also be used herefor, including agglomeration, extrusion, grinding and optionallyfollowed by sieving to obtain the required particle size distribution.

The inventors found another preferred way to provide elastomericcoatings on cores of water-swellable polymers, namely by providing acoating that has a significantly larger surface area than the outersurface area of the water-swellable polymer (core), so that when thepolymers swell, the coating can ‘unfold’ and extend. The inventors founda very easy and convenient way to provide such coated water-swellablepolymers, namely by applying the coating agent on water-swellablepolymers, which are in swollen state due to absorption of a liquid(e.g., water), and then removing the liquid or part thereof, so that thewater-swellable polymers (in the core) shrink again, but the coatingmaintains its original surface area. The surface area of the coating isthen larger than the surface area of the polymer core, and the coatingis then typically wrinkled; it can unwrinkle when the water-swellablepolymers absorb water and swell, without encountering any strain/stresson the coating due to the swelling of the water-swellable polymers.Thus, the coating agent is wet-extensible or elastomeric, without muchexposure to strain or stress and without the risk of rupturing.

A highly preferred process thus involves the step of obtainingwater-swellable polymers (particles) and immersing these in a dispersionor solution of an elastomeric material in a liquid that may comprise anamount of water to swell the water-swellable polymers, typically underthorough stirring.

The water-swellable polymers may absorb the liquid, and thereby, theelastomeric material is automatically ‘transferred’ to the surface ofwater-swellable polymers (particles). The amount of water-swellablepolymers and amount of liquid, including water, and elastomeric materialcan be adjusted such that the water-swellable polymers can absorb aboutall water present in the solution or dispersion and that when this isachieved, the water-swellable polymers, coated with elastomericmaterial, are in the form of gel “particles”. The resulting coating istypically under zero strain/stress.

The process may also involve addition of further processing aids in anyof the steps, such as granulation aids, flow aids, drying aids. For sometypes of coating agents, the coated water-swellable polymers maypotentially form agglomerates. Any flow aids known in the art may beadded (for example, prior to or during the coating step, or preferablyduring the drying and/or annealing step, as discussed below; for exampleAerosil 200, available from Degussa has been found to be a good flowaid).

Highly preferred may be that the process involves addition of aspreading aid and/or surfactant, as described above, which facilitatesthe coating step b).

Use

The water-swellable materials of the invention are useful in a number ofapplications, including in absorbent structures such as disposableabsorbent articles, such as preferably interlabial products, sanitarynapkins, panty liners, and preferably adult incontinent products, babydiapers, nappies and training pants. However, the present invention doesnot relate to such absorbent structures listed herein.

PROCESS EXAMPLES AND MATERIALS MADE BY THE PROCESS Preparation ofWater-Swellable Polymers that are Especially Useful for Use in ProcessStep a) of the Invention Example 1.1 Process for Preparation ofSpherical Water-Swellable Polymer Particles

Spherical core polymer particles may be obtained UMSICHT (FraunhoferInstitut Umwelt- Sicherheits-, Energietechnik, Oberhausen, Germany), ormade by following the adapted procedure below:

40 g glacial acrylic acid (AA) is placed into a beaker, and 1712 mgMethyleneBisAcrylAmide (MBAA ) is dissolved in the acid. Separately,13.224 g solid NaOH is dissolved in 58.228 g water and cooled. The NaOHsolution is then slowly added to the acrylic acid, and the resultingsolution is chilled to 4-10° C.

In a second beaker, 400 mg ammoniumperoxodisulfate (APS) and 400 mgsodiummetabisulfite are mixed and dissolved in 99.2 ml water. Thissolution is also chilled to 4-10° C.

With the use of two equal peristaltic pumps, both solutions are combinedand pumped at equal rates through a short static mixer unit, after whichthey are dropped as individual droplets into 60-80° C. hot silicone oil(Roth M 50, cat. # 4212.2) which is in a heated, about 2 m long, glasstube. The pump rate is adjusted such that individual droplets sinkthrough the oil in the tube, while also avoiding prematurepolymerization in the mixer unit. The polymerization proceeds during thedescent of the droplets through the oil, and particles (gelled polymerdroplets) are formed, which can be collected in a heated 1 literErlenmeyer flask attached to the bottom of the tube.

After completion of the addition, the oil is allowed to cool, and thespheres are collected by draining the oil. Excess oil is removed bywashing with i-propanol, and the particles (spheres) are pre-dried byexposing them to excess i-propanol for 12-24 hours. Additional washingswith i-propanol may be needed to remove traces of the silicone oil. Theparticles (spheres) are then dried in a vacuum oven at 60-100° C. untila constant weight is obtained.

The amount of MBAA may be adjusted, depending on what properties arerequired from the resulting polymers, e.g., when 0.3 mol % (per mol AA)MBAA is used, the resulting water-swellable polymer particles have aCCRC of about 50 g/g (absorption of 0.9% saline solution, as determinedby methods known in the art and described herein); when 1.0 mol % (permol AA) MBAA is used, the resulting water-swellable polymer particleshave a CCRC of about 19 g/g; when 2.0 mol % (per mol AA) MBAA is used,the resulting water-swellable polymer particles have a CCRC of about 9g/g.

All compounds were obtained by Aldrich Chemicals, and used withoutfurther purification.

Example 1.2 Process for the Preparation of Water-Swellable PolymersUseful Herein

To 300 g of glacial acrylic acid (AA), an appropriate amount of the corecrosslinker (e.g., MethyleneBisAcrylAmide, MBAA) is added (see above)and allowed to dissolve at ambient temperature. A 2500 ml resin kettle(equipped with a four-necked glass cover closed with septa, suited forthe introduction of a thermometer, syringe needles, and optionally amechanical stirrer) is charged with this acrylic acid /crosslinkersolution. Typically, a magnetic stirrer, capable of mixing the wholecontent, is added. An amount of water is calculated so that the totalweight of all ingredients for the polymerization equals 1500 g (i.e.,the concentration of AA is 20 w/w-%). 300 mg of the initiator (“V50”from Waco Chemicals) are dissolved in approx. 20 ml of this calculatedamount of deionized water. Most of the water is added to the resinkettle, and the mixture is stirred until the monomer and water are wellmixed. Then, the initiator solution is added together with any remainingwater. The resin kettle is closed, and a pressure relief is provided,e.g., by puncturing two syringe needles through the septa. The solutionis then spurged vigorously with argon via an 80 cm injection needlewhile stirring at 300 RPM. Stirring is discontinued after ˜8 minutes,while argon spurging is continued. The solution typically starts to gelafter 12-20 minutes total. At this point, persistent bubbles form on thesurface of the gel, and the argon injection needle is raised above thesurface of the gel. Purging with argon is continued at a lowered flowrate. The temperature is monitored, typically it rises from 20° C. to60-70° C. within an hour. Once the temperature drops below 60° C., thekettle is transferred into a circulation oven and kept at 60° C. for15-18 hours.

After this time, the resin kettle is allowed to cool, and the resultinggel is removed into a flat glass dish. The gel is then broken or cutwith scissors into small pieces (for example in pieces smaller than 2 mmmax. dimension), and transferred into a 6 liter glass beaker. The amountof NaOH (50%) needed to neutralize 75% of the acid groups of the polymeris diluted with deionized water to 2.5 liters, and added quickly to thegel. The gel is stirred until all the liquid is absorbed; then, it iscovered and transferred into a 60° C. oven and let equilibrate for 2days.

After this time, the gel is allowed to cool, then divided up into 2 flatglass dishes, and transferred into a vacuum oven, where it is dried at100° C./max. vacuum. Once the gel has reached a constant weight (usually3 days), it is ground using a mechanical mill (e.g., IKA mill) andsieved to obtain water-swellable polymer particles of the requiredparticle size, e.g., 150-800 μm.

(At this point, key parameters of the water-swellable polymer as usedherein may be determined).

The amount of MBAA may be adjusted, depending on what properties arerequired from the resulting polymers, e.g., when 0.01 mol % (per mol AA)MBAA is used, the resulting water-swellable polymer particles have aCCRC of about 90 g/g (absorption of 0.9% saline solution, as determinedby methods known in the art and described herein); when 0.03 mol % (permol AA) MBAA is used, the resulting water-swellable polymer particleshave a CCRC of about 73 g/g; when 0.1 mol % (per mol AA) MBAA is used,the resulting water-swellable polymer particles have a CCRC of about 56g/g; when 2.0 mol % (per mol AA) MBAA is used, the resultingwater-swellable polymer particles have a CCRC of about 16 g/g; when 5.0mol % (per mol AA) MBAA is used, the resulting water-swellable polymerparticles have a CCRC of about 8 g/g.

(All compounds were obtained by Aldrich Chemicals, and used withoutpurification.)

Example 1.3 Surface Cross-Linking Process Step

This example demonstrates surface crosslinking of water-swellablepolymers prior to subjecting them to the process step b) of theinvention. A 150 ml glass beaker is equipped with a mechanical stirrerwith a plastic blade, and charged with 4 g of a dry water-swellablepolymer in particulate form. The mechanical stirrer is selected in sucha way that a good fluidization of the polymers can be obtained at300-500 RPM. A 50-200 μl syringe is charged with a 4% solution (w/w) ofDENACOL (=Ethylene Glycol DiGlycidyl Ether=EGDGE) in 1,2-propanediol;another 300 μl syringe is charged with deionised water.

The water-swellable polymers are fluidized in the beaker at approx. 300RPM, and the surface cross-linking agent is added within 30 seconds.Mixing is continued for a total of three minutes. While stirring iscontinued, 300 μl of water are then added within 3-5 seconds, andstirring is continued at 300-500 RPM for another 3 minutes. After thistime, the mixture is transferred into a glass vial, sealed with aluminumfoil, and let equilibrate for 1 hour. Then the vial is transferred to a140° C. oven, and kept at this temperature for 120 minutes. After thistime, the vial is allowed to cool, the contents are removed, and thesurface cross-linked water-swellable polymer is obtained. Anyagglomerates may be carefully broken by gentle mechanical action. Theresulting surface cross-linked water-swellable polymer particles maythen be sieved to the desired particle size.

The Following Examples Show Coating Processes That are used toDemonstrate the Coatings Step b) of the Process of the Invention

Example 2.1 Process of Providing Coated Water-Swellable Materials byDirectly Mixing them into a Water Based Dispersion of the ElastomericPhase-Separating Polymer

The following is a preferred process for making the water-swellablematerial of the invention, involving swelling the water-swellablepolymers prior to, or simultaneously with the coating step.

The amount of water-swellable polymers to be coated, coating level andwater needed to swell the water-swellable polymers is chosen.

Then, the dispersion or solution of the coating agent or elastomericmaterial is prepared by mixing an commercial available coating agent orelastomeric material and water with optionally THF under stirring, forexample in a glass beaker using magnetic stirrers at about 300 rpm forabout 5 minutes. At all times, care needs to be taken that no film isformed on the surface of the dispersion. Typically such dispersioncontains at the most 70% by weight of elastomeric polymer.

In order to monitor the coating process better, a staining color mightbe added to the dispersion, for example New Fuchsin Red.

Then, a mechanical stirrer with a double cross Teflon blade is used andthe dispersion is stirred such that a vortex can be seen, thewater-swellable polymer (particles) are quickly added under continuousstirring. Once the water-swellable polymers start absorbing the waterfrom the dispersion (typically after about 15 seconds), the mixture willstart to gel and the vortex will eventually disappear. Then, when aboutall of the free liquid has been absorbed, the stirring is stopped andthe resulting coated water-swellable polymers may be dried or posttreated by any of the methods described herein.

Example 2.2 Process of Providing Coated Water-Swellable Materials byDirectly Mixing them into an Elastomer Solution

The following is a preferred process for making the water-swellablematerial of the invention, involving swelling the water-swellablepolymers prior to, or simultaneously with the coating step.

The amount of water-swellable polymers to be coated, coating level andwater needed to swell the water-swellable polymers is chosen.

Then, the solution of the coating agent is prepared, by dissolving thecommercial available coating agent, such as Estane 58245 in an organicsolvent (e.g., THF or a mixture of water and THF, if required), forexample in a glass beaker for 1 hour to 24 hours.

In order to monitor the coating process better, a staining color mightbe added to the dispersion, for example New Fuchsin Red.

Then, this solution is added to the water-swellable polymer that isbeing stirred or mechanically agitated to provide the coating. When thefree liquid has been absorbed into the water-swellable polymer, thestirring is stopped and the resulting coated water-swellable polymersmay be dried or post treated by any of the methods described herein.

Example 2.3 Process of Providing Individually Coated Water-SwellableMaterials

An alternative preferred coating process of the invention is as follows:

The (solid, particulate) water-swellable polymers are placed on asurface that is preferably under an angle (30-45 degrees).

The coating agent, in the form of a solution, is applied in drops, e.g.,by use of a pipette or by spraying, onto the polymers. Hereby, no airbubbles should be formed.

Thus, a film is formed on the surface of the water-swellable polymers.

These coated water-swellable polymers are then dried, either at roomtemperature (20° C.), or for example at 40° C./80% humidity, for up to 2days, or for example in an oven (if required, a vacuum oven) at a lowtemperature (up to 70° C.).

The coated water-swellable material can then be annealed as describedbelow. It may then also be formed into the desired form, e.g.,particles.

Example 2.4 Alternative Preferred Coating Process

In another preferred process, a dispersion of the water-swellablepolymers is prepared first and the coating agent is added thereto.

For example, 200 grams of a water-swellable polymer (cross-linkedpolyacrylic acid based polymers, for example prepared by the methoddescribed above) is placed in a plastic beaker and n-heptane is added,until the heptane stands about 1-2 mm above the surface of the polymersin the beaker; this is typically about 100 g of n-heptane.

Using a household mixer (e.g., for whipping cream), the components aremixed at high speed. The coating agent, in the form of a solution of anelastomeric coating material, e.g., a polyurethane solution as describedabove, is added to the beaker with the water-swellable polymers by useof for example a pipette. The mixture is continuously stirred, avoidingthe formation of lumps.

The resulting material can be spread out over a surface as a thin layer(e.g., less than 1 cm) and allowed to air dry for at least 12 hours orin a (vacuum) oven (any temperature up to about 70° C.

After cooling or subsequent steps, the resulting material may bemechanically reduced or sieved to the desired particle sizes.

Example 2.5 Process of Providing Coated Water-Swellable Materials Usinga Fluidized Bed Wurster Coater

Step b) may also be done in a fluidized bed or Wurster coater.

For example, a Lakso Wurster Model 101 (The Lakso Company, Leominster,Mass.) may be used or a Glatt GPCG-3 granulator-coater may be used(supplied by Glatt Ingenieurtechnik GmbH, Nordstrasse 12, 99427 Weimar,Germany). It may be desired that the coating equipment is pre-heated,for example to 70° C., under air flow, for example for about 30 minutes.

For example, typically between 20 and 35 g of water-swellable polymer isplaced in the vessel.

The coating agent, preferably in fluid form, such as the polymersolutions/dispersions listed below, is placed in a container on thestirring platform and stirred using a magnetic bar at low speed toprevent entrainment of air. The weight can be recorded.

The peristaltic pump is calibrated and then set to the desired flow rate(e.g., 5 g/minute) and the direction of flow of the coating agent is setforward. The desired inlet air flow and temperature are set to 50 m3/hrand 60° C. Then, the ‘atomizing’ air supply and pump are started. Theoutlet temperature of the system is maintained at 45° C. by adjustingthe solvent flow rate into the system.

(A higher speed may be used to advance the coating agent closer towardsthe inlet of the coater and then setting the correct speed for theexperiment.)

The experiment is typically complete when stickiness prevents efficientfluidization of the powder (between 10 and 60 minutes).

Then, the coating agent flow is stopped immediately and flow reversed.The weight of coating agent used in the experiment is recorded.

Optionally, the resulting coated water-swellable polymers may be driedwithin the coater, which also may aid to reduce particle surfacestickiness (drying time typically between 5 and 60 minutes).

Then, the material inside the coater is weighed.

In general, the material may be returned to the coating vessel tocontinue the process, if required, e.g., if more than one coating agentis to be applied or to add a flow aid, e.g., 0.5-2% hydrophobic silica.

In general, a filler may be added (e.g., to the solution) to reducetackiness of the coated water-swellable material, for example 1-5% byweight of a filler with a median particle size of less 5 microns, tomake thin coatings with an average caliper of for example 5 microns to20 or even to 10 microns

In order to visualise the coating process, or for aesthetic purposes, acolouring agent or dye solution may be added to the coating agent, forexample New Fuchsin Red (0.25 g of New Fuchsin Red in 5 ml to 25 mldeionised water (15-25° C.), without entrainment of air bubbles). Thedye solution can be added drop-wise to about 10 ml of the coating agentunder stirring and this can then be stirred into the remaining coatingagent (sufficient for up to 70 ml coating agent).

The following water-swellable materials were made by the process above,using a fluid bed coater or Wurster coater; in each case, 500 g of theuncoated water-swellable polymers, available as ASAP 500 from BASF wasused and the specified amount of polymer, at the specified weight-%solids concentration, was used.

The coated samples were dried under vacuum for 24 h at room temperature.Polymer Amount Concentration of Polymer Example Polymer (% w/w) Solvent(% w/w) 1 Vector 4211 10 MEK 2.8 2 Vector 4211 12 MEK 5.5 3 Irogran654/5 5 MEK 1.4 4 Irogran 654/5 5 MEK 1.6 5 Septon 2063 10 Toluene 6.7 6Estane 58245 5 DMF 1.4

Vector is a trade name of Dexco Polymers, 12012 Wickchester Lane,Houston, Tex. 77079, USA; Irogran is a trade name of HuntsmanPolyurethanes, 52 Kendall Pond Road, Derry, N.H. 03038, USA; Septon is atrade name of the Septon Company of America, A Kuraray Group Company,11414 Choate Road, Pasadena, Tex. 77507, USA; Estane is a trade name ofNoveon Inc, 9911 Brecksville Road, Cleveland, Ohio 44141-3247, USA.

Example 2.6 Preferred Subsequent Process Steps of Drying and/orAnnealing

The process of the invention may comprise a step whereby a solution,suspension or dispersion or solution is used, e.g., whereby thewater-swellable polymers comprise a liquid (water) or whereby thecoating agent is in the form of a dispersion, suspension or solution.

The following is a preferred process step of drying the coatedwater-swellable polymers of step b):

The coated water-swellable material comprising a liquid, e.g., water, isplaced on a surface, for example, it is spread out in a Pyrex glass panin the form of a layer which is not more than about 1 cm thick. This isdried at about 50° Celsius for at least 12 hours.

If the amount of liquid present in the coated water-swellable polymersis known, then, by measuring the coated water-swellable materialcomprising said weight of liquid prior to drying and then subsequentlyafter drying, one can determine the residual moisture in the resultingwater-swellable material (coated water-swellable polymers) as known inthe art. Typically, the resulting water-swellable material/coatedwater-swellable polymers will be dried to less than 5% (by weight of thematerial) moisture content.

The coated water-swellable polymers or material may subsequently beannealed, as described herein.

For some type of coating agents, coated water-swellable polymers maypotentially form agglomerates. Flow aids may be added prior to or duringthe coating step, or preferably during the drying and/or annealing stepas known in the art, e.g., Aerosil 200, available from Degussa.

The above drying step may also be done by spreading the coatedwater-swellable polymers on a Teflon coated mesh in a very thin layer,e.g., less than 5 mm, such as to enable convection through the layer.

As alternative method, the coated water-swellable polymers that containa liquid (water), may also be directly dried and annealed in one step,e.g., placing the material in a vacuum oven at 120 or 140 Celsius for 2hours, or at a temperature that is appropriate for the polymer that isused as determined by the thermal transitions that occur for thatpolymer.

Example 2.7 Example: Method of Drying in Fluidized Bed

A Lakso Wuster coater as used in example 2.5 and other fluidized beddriers known in the art may also be used to dry the coated materialsformed by step b) of the process. For example, the conditions of example2.5 might be used, introducing the coated material (and thus using theWurster coating equipment only for drying the coated material).

Example 2.8 Method of Azeotropic Distillation and Drying

The wet, coated polymers may be dried or dewatered at low-temperaturevia azeotropic distillation from a suitable liquid, which does notdissolve the coating agent, for example, cyclohexane, provided thecoating agent does not dissolve in cyclohexane. For example, the coatedpolymers are transferred to a 2 liter resin kettle, equipped with aTrubore mechanical stirrer with Teflon blade and digital stirring motor,immersion thermometer, and Barrett type moisture receiver with graduatedsidearm and water-cooled condenser. Approximately one liter ofcyclohexane is added to the resin kettle. While stirring, a heatingmantle is used to raise the temperature of the stirred cyclohexane/gelsystem to reflux. Heating and reflux is continued until the temperatureof the system approaches the boiling point of cyclohexane (approximately80° C.) and only minimal additional quantity of water is delivered tothe sidearm. The system is cooled and then filtered to obtain thedewatered or dried coated water-swellable polymers, which may be furtherdried overnight under vacuum at ambient temperature (20° C.).

Test Methods Used Herein:

Preparation of Films of the Coating Agent

In order to subject the coating agents or phase-separating elastomericmaterial used herein to some of the test methods below, including theWet-elongation test, films need to be obtained of said coating agents orphase separating elastomeric material thereof.

The preferred average (as set out below) caliper of the (dry) films forevaluation in the test methods herein is around 60 μm.

Methods to prepare films are generally known to those skilled in the artand typically comprise solvent casting, hot melt extrusion or meltblowing films. Films prepared by these methods may have a machinedirection that is defined as the direction the film is drawn or pulled.The direction perpendicular to the machine direction is defined as thecross-direction.

For the purpose of the invention, the films used in the test methodsbelow are formed by solvent casting, except when the coating agent orphase-separating material cannot be made into a solution or dispersionof any of the solvents listed below, and then the films are made byhotmelt extrusion as described below. (The latter is the case whenparticulate matter from the phase-separating material is still visiblein the mixture of the material or coating agent and the solvent, afterattempting to dissolve or disperse it at room temperature for a periodbetween 2 to 48 hours, or when the viscosity of the solution ordispersion is too high to allow film casting.)

It should be understood that in the first embodiment of the invention,when an annealing step is only optional, the films are prepared withoutthe annealing step. If the annealing step is required, then the films tobe tested are made by a process below, involving an annealing step aswell.

The resulting film should have a smooth surface and be free of visibledefects such as air bubbles or cracks.

An Example to Prepare a Solvent Cast Film Herein from a Phase-SeparatingElastomeric Material or Coating Agent:

The film to be subjected to the tests herein can be prepared by castinga film from a solution or dispersion of said material or coating agentas follows:

The solution or dispersion is prepared by dissolving or dispersing thephase-separating material or coating agent, at 10 weight %, in water, orif this is not possible, in THF (tetrahydrofuran), or if this is notpossible, in dimethylformamide (DMF), or if this is not possible inmethyl ethyl ketone (MEK), or if this is not possible, indichloromethane or if this is not possible in toluene, or if this is notpossible in cyclohexane (and if this is not possible, the hotmeltextrusion process below is used to form a film).

Next, the dispersion or solution is poured into a Teflon boat withaluminum foil to slow evaporation, and the solvent or dispersant isslowly evaporated at a temperature above the minimum film formingtemperature of the polymer, typically about 25° C., for a long period oftime, e.g., during at least 48 hours, or even up to 7 days . Then, thefilms are placed in a vacuum oven for 6 hours, at 25° C., to ensure anyremaining solvent is removed.

The Process to Prepare a Hotmelt Extruded Film Herein is as Follows:

If the solvent casting method is not possible, films of the coatingagent or phase-separating material herein may be extruded from a hotmelt using a rotating single screw extrusion set of equipment operatingat temperatures sufficiently high to allow the material or coating agentto flow. If the material or coating agent has a melting temperature Tm,then the extrusion should takes place at least 20° C. above said Tm. Ifthe material or coating agent is amorphous (i.e., does not have a Tm),steady shear viscometry can be performed to determine the order todisorder transition for the material, or the temperature where theviscosity drops dramatically. The direction that the film is drawn fromthe extruder is defined as the machine direction and the directionperpendicular to the drawing direction is defined as the crossdirection. Wet-extensible For example material Die Temperature Screw rpm7 Irogran VP 654/5 180° C. 40 8 Elastollan LP 9109 170° C. 30 9 Estane58245 180° C. 30 10 Estane 4988 180° C. 30 11 Pellethane 2103-70A 185°C. 30Annealing of the Films:

If the process herein involves an annealing step, and if thewater-swellable material herein comprises an annealed coating, then thefilms used in the test method are annealed. This annealing of the films(prepared and dried as set out above) should, for the purpose of thetest methods below, be done by placing the film in a vacuum oven at atemperature which is about 20° C. above the highest Tg of the usedcoating agent or used phase-separating elastomeric material, and this isdone for 2 hours in a vacuum oven at less than 0.1 Torr, provided thatwhen the coating agent or elastomeric material has a melting temperatureTm, the annealing temperature is at least 20° C. below the Tm, and thenpreferably (as close to) 20° C. above the highest Tg. When the Tg isreached, the temperature should be increased slowly above the highest Tgto avoid gaseous discharge that may lead to bubbles in the film. Forexample, a material with a hard segment Tg of 70° C. might be annealedat 90° C. for 10 min, followed by incremental increases in temperatureuntil the annealing temperature is reached.

If the coating agent or phase-separating material has a Tm, then saidannealing of the films (prepared as set out above and to be tested bythe methods below) is done at a temperature which is above the (highest)Tg and at least 20° C. below the Tm and (as close to) 20° C. above the(highest) Tg. For example, a wet-extensible material that has a Tm of135° C. and a highest Tg (of the hard segment) of 100° C., would beannealed at 115° C.

Removal of Films, if Applicable

If the dried and optionally annealed films are difficult to remove fromthe film forming substrate, then they may be placed in a warm water bathfor 30 s to 1 min to remove the films from the substrate. The film isthen subsequently dried for 6-24 h at 25° C.

Wet-Elongation Test and Wet-Tensile-Stress Test:

This test method is used to measure the wet-elongation at break(=extensibility at break) and tensile properties of films ofphase-separating material or coating agents as used herein, by applyinga uniaxial strain to a flat sample and measuring the force that isrequired to elongate the sample. The film samples are herein strained inthe cross-direction, when applicable.

A preferred piece of equipment to do the tests is a tensile tester suchas a MTS Synergie100 or a MTS Alliance available from MTS SystemsCorporation 14000 Technology Drive, Eden Prairie, Minn., USA, with a 25Nor 50N load cell. This measures the Constant Rate of Extension in whichthe pulling grip moves at a uniform rate and the force measuringmechanisms moves a negligible distance (less than 0.13 mm) withincreasing force. The load cell is selected such that the measured loads(e.g., force) of the tested samples will be between 10 and 90% of thecapacity of the load cell.

Each sample is die-cut from a film, each sample being 1×1 inch (2.5×2.5cm), as defined above, using an anvil hydraulic press die to cut thefilm into sample(s) (Thus, when the film is made by a process that doesnot introduce any orientation, the film may be tested in eitherdirection.). Test specimens (minimum of three) are chosen which aresubstantially free of visible defects such as air bubbles, holes,inclusions, and cuts. They must also have sharp and substantiallydefect-free edges.

The thickness of each dry specimen is measured to an accuracy of 0.001mm with a low pressure caliper gauge such as a Mitutoyo Caliper Gaugeusing a pressure of about 0.7 kPa. Three different areas of the sampleare measured and the average caliper is determined. The dry weight ofeach specimen is measured using a standard analytical balance to anaccuracy of 0.001 g and recorded. Dry specimens are tested withoutfurther preparation for the determination of dry-elongation, dry-secantmodulus, and dry-tensile stress values used herein.

For wet testing, pre-weighed dry film specimens are immersed in salinesolution [0.9% (w/w) NaCl] for a period of 24 hours at ambienttemperature (23+/−2° C.). Films are secured in the bath with a 120-meshcorrosion-resistant metal screen that prevents the sample from rollingup and sticking to itself. The film is removed from the bath and blotteddry with an absorbent tissue such as a Bounty™ towel, to remove excessor non-absorbed solution from the surface. The wet caliper is determinedas noted for the dry samples. Wet specimens are used for tensile testingwithout further preparation. Testing should be completed within 5minutes after preparation is completed. Wet specimens are evaluated todetermine wet-elongation, wet-secant modulus, and wet-tensile stress.

For the purpose of the present invention the Elongation to (or at) Breakwill be called Wet-elongation to (or at) Break and the tensile stress atbreak will be called Wet Stress at Break. (At the moment of break, theelongation to break % is the wet extensibility at break as used herein.)

Tensile testing is performed on a constant rate of extension tensiletester with computer interface such as an MTS Alliance tensile testerwith Testworks 4 software. Load cells are selected such that measuredforces fall within 10-90% of the cell capacity. Pneumatic jaws, fittedwith flat 2.54 cm-square rubber-faced grips, are set to give a gagelength of 2.54 cm. The specimen is loaded with sufficient tension toeliminate observable slack, but less than 0.05N. The specimens areextended at a constant crosshead speed of 25.4 cm/min until the specimencompletely breaks. If the specimen breaks at the grip interface orslippage within the grips is detected, then the data is disregarded andthe test is repeated with a new specimen and the grip pressure isappropriately adjusted. Samples are run in triplicate to account forfilm variability.

The resulting tensile force-displacement data are converted tostress-strain curves using the initial sample dimensions from which theelongation, tensile stress, and modulus that are used herein arederived. Tensile stress at break is defined as the maximum stressmeasured as a specimen is taken to break, and is reported in MPa. Thebreak point is defined as the point on the stress-strain curve at whichthe measured stress falls to 90% of its maximum value. The elongation atbreak is defined as the strain at that break point and is reportedrelative to the initial gauge length as a percentage. The secant modulusat 400% elongation is defined as the slope of the line that intersectsthe stress-strain curve at 0% and 400% strain. Three stress-straincurves are generated for each extensible film coating that is evaluated.Elongation, tensile stress, and modulus used herein are the average ofthe respective values derived from each curve.

The dry secant elastic modulus at 400% elongation (SM_(dry400%)) iscalculated by submitting a dry film, as obtainable by the methodsdescribed above (but without soaking it in the 0.9% NaCl solution), tothe same tensile test described above, and then calculating the slope ofthe line intersecting with the zero intercept and the stress-straincurve at 400%, as done above.

Glass Transition Temperatures

Glass Transition Temperatures (Tg's) are determined for the purpose ofthis invention by differential scanning calorimetry (DSC). Thecalorimeter should be capable of heating/cooling rates of at least 20°C./min over a temperature range, which includes the expected Tg's of thesample that is to be tested, e.g., of from −90° to 250° C., and thecalorimeter should have a sensitivity of about 0.2 μW. TA InstrumentsQ1000 DSC is well-suited to determining the Tg's referred to herein. Thematerial of interest can be analyzed using a temperature program suchas: equilibrate at −90° C., ramp at 20° C./min to 120° C., holdisothermal for 5 minutes, ramp 20° C./min to −90° C., hold isothermalfor 5 minutes, ramp 20° C./min to 250° C. The data (heat flow versustemperature) from the second heat cycle is used to calculate the Tg viaa standard half extrapolated heat capacity temperature algorithm.Typically, 3-5 g of a sample material is weighed (+/_(—)0.1 g) into analuminum DSC pan with crimped lid.

As used herein Tg₁ will be a lower temperature than Tg₂.

Polymer Molecular Weights

Gel Permeation Chromatography with Multi-Angle Light ScatteringDetection (GPC-MALS) may be used for determining the molecular weight ofthe phase-separating polymers herein. Molecular weights referred toherein are the weight-average molar mass (Mw). A suitable system formaking these measurements consists of a DAWN DSP Laser Photometer (WyattTechnology), an Optilab DSP Interferometric Refractometer (WyattTechnology), and a standard HPLC pump, such as a Waters 600E system, allrun via ASTRA software (Wyatt Technology).

As with any chromatographic separation, the choice of solvent, column,temperature and elution profiles and conditions depends upon thespecific polymer which is to be tested. The following conditions havebeen found to be generally applicable for the phase-separating polymersreferred to herein: Tetrahydrofuran (THF) is used as solvent and mobilephase; a flow rate of 1 mL/min is passed through two 300×7.5 mm, 5 μm ,PLgel, Mixed-C GPC columns (Polymer Labs) which are placed in series andare heated to 40-45° C. (the Optilab refractometer is held at the sametemperature); 100 μL of a 0.2% polymer solution in THF solution isinjected for analysis. The dn/dc values are obtained from the literaturewhere available or calculated with ASTRA utility. The weight-averagemolar mass (Mw) is calculated by with the ASTRA software using the Zimmfit method.

Moisture Vapor Transmission Rate Method (MVTR Method)

MVTR method measures the amount of water vapor that is transmittedthrough a film under specific temperature and humidity. The transmittedvapor is absorbed by CaCl₂ desiccant and determined gravimetrically.Samples are evaluated in triplicate, along with a reference film sampleof established permeability (e.g., Exxon Exxaire microporous material#XBF-110W) that is used as a positive control.

This test uses a flanged cup (machined from Delrin (McMaster-CarrCatalog #8572K34) and anhydrous CaCl₂ (Wako Pure Chemical Industries,Richmond, Va.; Catalog 030-00525). The height of the cup is 55 mm withan inner diameter of 30 mm and an outer diameter of 45 mm. The cup isfitted with a silicone gasket and lid containing 3 holes for thumbscrews to completely seal the cup. Desiccant particles are of a size topass through a No. 8 sieve but not through a No. 10 sieve. Filmspecimens approximately 3.8 cm×6.4 cm that are free of obvious defectsare used for the analysis. The film must completely cover the cupopening, A, which is 0.0007065 m².

The cup is filled with CaCl₂ to within 1 cm of the top. The cup istapped on the counter 10 times, and the CaCl₂ surface is leveled. Theamount of CaCl₂ is adjusted until the headspace between the film surfaceand the top of the CaCl₂ is 1.0 cm. The film is placed on top of the cupacross the opening (30 mm) and is secured using the silicone gasket,retaining ring, and thumb screws. Properly installed, the specimenshould not be wrinkled or stretched. The sample assembly is weighed withan analytical balance and recorded to ±0.001 g. The assembly is placedin a constant temperature (40±3° C.) and humidity (75±3% RH) chamber for5.0 hr±5 min. The sample assembly is removed, covered with Saran Wrap®and is secured with a rubber band. The sample is equilibrated to roomtemperature for 30 min, the plastic wrap removed, and the assembly isreweighed and the weight is recorded to ±0.001 g. The absorbed moistureM_(a) is the difference in initial and final assembly weights. MVTR, ing/m²/24 hr (g/m²/day), is calculated as:MVTR=M _(a)(A*0.208 day)Replicate results are averaged and rounded to the nearest 100 g/m²/24hr, e.g., 2865 g/m²/24 hr is herein given as 2900 g/m²/24 hr and 275g/m²/24 hr is given as 300 g/m²/24 hr.Method of Determining the Water Swellability Capacity of Wet-ExtensibleMaterials Used Herein, Considered Non-Water-Swellable

The elastomeric material herein is non-water swelling and /or absorbing,which means that it absorbs typically less than 1 g water/g material, oreven less than 0.5 g/g or even less than 0.2 g/g or even less than 0.1g/g.

The water absorption can be determined as follows.

A certain, pre-weighed amount of the elastomeric material (sample), withweight M (sample), is immersed in an excess amount of deionized waterand is allowed to ‘absorb’ water for about 2.5 hours.

The sample is gently removed from the water; if possible, excess wateris blotted from the sample with tissue towel for few seconds. The sampleis then weighed again and the wet sample weight M (sample-wet) isdetermined.

The water absorption capacity of the sample, X (AC sample), isdetermined by the following formula:X(AC sample)={M(sample wet)−M(sample)}/M(sample)The value X is reported in gram of absorbed fluid per gram of dry filmsample.

The water absorption as determined is herein also called WaterSwellability (or Swelling) Capacity of the phase-separating elastomericmaterial.

Cylinder Centrifuge Retention Capacity

The Cylinder Centrifuge Retention Capacity (CCRC) method determines thefluid retention capacity of the water-swellable materials or polymers(sample) after centrifugation at an acceleration of 250 g. Prior tocentrifugation, the sample is allowed to swell in excess saline solutionin a rigid sample cylinder with mesh bottom and an open top.

This method is particularly applicable to materials having fluidretention capacities that are substantially higher than 40 g/g andconsequently not well-suited to evaluation by tea bag methods (e.g.,EDANA 441.2-02, U.S. Pat. No. 6,359,192 B1, U.S. Pat. No. 5,415,643).Duplicate sample specimens are evaluated for each material tested andthe average value is reported.

The CCRC can be measured at ambient temperature by placing the samplematerial (1.0+/−0.001 g) into a pre-weighed (+/−-0.01 g) Plexiglassample container that is open at the top and closed on the bottom with astainless steel mesh (400) that readily allows for saline flow into thecylinder but contains the absorbent particles being evaluated. Thesample cylinder approximates a rectangular prism with rounded-edges inthe 67 mm height dimension. The base dimensions (78×58 mm OD, 67.2×47.2MM ID) precisely match those of modular tube adapters, herein referredto as the cylinder stand, which fit into the rectangular rotor buckets(Heraeus # 75002252, VWR # 20300-084) of the centrifuge (HeraeusMegafuge 1.0; Heraeus # 75003491, VWR # 20300-016).

The loaded sample cylinders are gently shaken to evenly distribute thesample across the mesh surface and then placed upright in a pancontaining saline solution. The cylinders should be positioned to ensurefree flow of saline through the mesh bottom. Cylinders should not beplaced against each other or against the wall of the pan, or sealedagainst the pan bottom. The sample is allowed to swell, withoutconfining pressure and in excess saline, for a time that corresponds to80% of the CCRC saturation or equilibrium time for the specific materialunder study. The saturation time is determined from a plot of CCRCvalues versus increasing swell time (60 minute increments). As usedhere, saturation time is defined as the swell time required to reach thesaturation/equilibrium CCRC value. The saturation value is determined bysequentially calculating the standard deviation (SD) of the CCRC valuesof three consecutive points on the curve (the first SD calculatedcorresponds to time points 1-3, the second SD to time points 24, thethird SD to time points 3-5, and so on). The saturation value is definedas the largest of the three consecutive CCRC values having a standarddeviation of less than 2.

Cylinders are immediately removed from the solution. Each cylinder isplaced (mesh side down) onto a cylinder stand and the resulting assemblyis loaded into the rotor basket such that the two sample assemblies arein balancing positions in the centrifuge rotor.

The samples are centrifuged for 3 minutes (±10 s) after achieving therotor velocity required to generate a centrifugal acceleration of 250±5g at the bottom of the cylinder stand. The openings in the cylinderstands allow any solution expelled from the absorbent by the appliedcentrifugal forces to flow from the sample to the bottom of the rotorbucket where it is contained. The sample cylinders are promptly removedafter the rotor comes to rest and weighed to the nearest 0.01 g.

The cylinder centrifuge retention capacity expressed as grams of salinesolution absorbed per gram of sample material is calculated for eachreplicate as follows:${CCRC} = {\frac{m_{CS} - \left( {m_{Cb} + m_{S}} \right)}{m_{S}}\quad\left\lbrack \frac{g}{g} \right\rbrack}$where:

-   m_(CS): is the mass of the cylinder with sample after centrifugation    [g]-   m_(Cb): is the mass of the dry cylinder without sample [g]-   m_(S): is the mass of the sample without saline solution [g]

The CCRC referred to herein is the average of the duplicate samplesreported to the nearest 0.01 g/g.

Saline Flow Conductivity (SFC)

A measure of permeability and an indication of porosity is provided bythe saline flow conductivity of the gel bed as described in U.S. Pat.No. 5,562,646, (Goldman et al.) issued Oct. 8, 1996 (whereby however a0.9% NaCl solution is used instead of Jayco solution).

Extractables or Extractable Polymers Value

Another important characteristic of particularly preferredwater-swellable materials and the water-swellable polymers useful in thepresent invention is the level of extractable polymer material orextractables present therein. Evaluation and explanation of which levelsof extractable polymer is still acceptable is disclosed and explained indetail in U.S. Pat. No. 4,654,039. As a general rule the extractableamount should be as low as possible and the lower it is the lessundesired reaction the extractable material can cause. Preferred arelevels of extractables of less than 10% by weight, or even less than 5%or even less than 3% (1 hour test values).

Method to Determine the Free Swell Rate of Water-Swellable MaterialsHerein

This method serves to determine the swell rate of the water-swellablematerials herein in a 0.9% saline solution, without stirring orconfining pressure. The amount of time taken to absorb a certain amountof fluid is recorded and this is reported in gram of fluid (0.9% saline)absorbed per gram of water-swellable material per second, e.g., g/g/sec.

The saline solution is prepared by adding 9.0 gram of NaCl into 100 mldistilled, deionized water, and this is stirred until all NaCl isdissolved.

The sample material (1.0 g+/−0.001 g) is weighed and placed evenly overthe bottom of a 25 ml beaker. A 20.0 ml aliquot of the saline solution(also at 23° C.) is promptly poured into the beaker. A timer is startedimmediately after the saline solution is delivered and stopped when thefinal portion of the fluid phase coalesces with the swelling sample.

This is readily indicated by the loss of light reflection from the bulksaline surface, particularly at the interface with the beaker walls. Theelapsed time, t_(s), in seconds is recorded. The free swell rate, in gliquid/g sample material/sec, is calculated as: FSR=20/t_(s). The testis run in triplicate and the average is used for the free swell rate ofthe sample material.

Determination of the Coating Caliper and Coating Caliper Uniformity

Elastomeric coatings on water-swellable polymers or materials as usedherein can typically be investigated by standard scanning electronmicroscopy, preferably environmental scanning electron microscopy (ESEM)as known to those skilled in the art. In the following method the ESEMevaluation is also used to determine the average coating caliper and thecoating caliper uniformity of the coated water-swellablepolymers/materials via cross-section of the materials.

Equipment model: ESEM XL 30 FEG (Field Emission Gun)

ESEM setting: high vacuum mode with gold covered samples to obtain alsoimages at low magnification (35×) and ESEM dry mode with LFD (largeField Detector which detects ˜80% Gaseous Secondary Electrons+20%Secondary Electrons) and bullet without PLA (Pressure Limiting Aperture)to obtain images of the coating/shells as they are (no gold coveragerequired).

Filament Tension: 3 KV in high vacuum mode and 12 KV in ESEM dry mode.

Pressure in Chamber on the ESEM dry mode: from 0.3 Torr to 1 Torr ongelatinous samples and from 0.8 to 1 Torr for other samples.

Samples of coated water-swellable material or polymers or of uncoatedpolymers can be observed after about 1 hour at ambient conditions (20C., 80% relative humidity) using the standard ESEM conditions/equipment.

Then, the same samples can be observed in high vacuum mode. Then thesamples can be cut via a cross-sectional cut with a Teflon blade (Teflonblades are available from the AGAR scientific catalogue (ASSING) withreference code T5332), and observed again under vacuum mode.

The coatings have different morphology than the uncoated water-swellablepolymers and the coatings are clearly visible in the ESEM images, inparticular when observing the cross-sectional views.

The average coating caliper is determined then by analyzing at least 5particles of the water-swellable material or coated water-swellablepolymer and determining 5 average calipers, an average per particle (byanalyzing the cross-section of each particle and measuring the caliperof the coating in at least 3 different areas) and taking then theaverage of these 5 average calipers.

The uniformity of the coating is determined by determining the minimumand maximum caliper of the coating via ESEM of the cross-sectional cutsof at least 5 different particles and determining the average (over 5)minimum and average maximum caliper and the ratio thereof.

If the coating is not clearly visible in ESEM, then staining techniquesknown to the skilled in the art that are specific for the coatingapplied may be used such as enhancing the contrast with osmiumtetraoxide, potassium permanganate and the like, e.g., prior to usingthe ESEM method.

Method to Determine the Theoretical Equivalent Shell Caliper of theWater-Swellable Material Herein

If the amount of coating agent comprised in the water-swellable materialis known, a theoretical equivalent average caliper may be determined asdefined below.

This method calculates the average caliper of a coating layer or shellon the water-swellable material herein, under the assumption that thewater-swellable material is to be monodisperse and spherical (which maynot be the case in practice).

Key Parameters Symbol INPUT Parameter Mass Median Particle Size of theD_AGM_dry water-swellable polymer(AGM) prior to coating (also called“average diameter”) Intrinsic density of the base Rho_AGM_intrinsicwater-swellable bulk polymer (without coating) Intrinsic density of thephase-separating Rho_polymer shell elastomeric polymer (coating or shellonly) Coating (shell) Weight Fraction of the c_shell_per_total Coatedwater-swellable polymer (Percent of coating as percent of total coatedwater-swellable polymer) OUTPUT Parameters Average coating caliper ifthe water- d_shell swellable polymer is monodisperse and spherical MassMedian Particle Size of D_AGM_coated the Coated water-swellable polymer(“average diameter after coating”) Coating Weight Ratio as Percentc_shell_to_bulk of Polymer Coating in percent of uncoatedwater-swellable polymer weightFormulas

(note: in this notation: all c which are in percent have ranges of 0 to1 which is equivalent 5 to 0 to 100%.)${d\_ shell}:={{{\frac{{D\_ AGM}{\_ dry}}{2} \cdot \left\lbrack {\left\lbrack {1 + {\frac{{c\_ shell}{\_ per}{\_ total}}{\left( {1 - {{c\_ shell}{\_ per}{\_ total}}} \right)} \cdot \frac{{Rho\_ AGM}{\_ intrinsic}}{{Rho\_ polymer}{\_ shell}}}} \right\rbrack^{\frac{1}{3}} - 1} \right\rbrack}\quad{D\_ coated}{\_ AGM}}:={{{D\_ AGM}{\_ dry}} + {2 \cdot {d\_ shell}}}}$${{c\_ shell}{\_ to}{\_ bulk}}:=\frac{{c\_ shell}{\_ per}{\_ total}}{1 - {{c\_ shell}{\_ per}{\_ total}}}$

Example

D_AGM_dry: = 0.4 mm (400 μm); Rho_AGM_intrinsic: = Rho_polymer_shell: =1.5 g/cc C_shell_(—) 1 2 5 10 20 30 40 50 per_total [%] C_shell_(—) 1.02.0 5.3 11 25 43 67 100 to_bulk [%] d_shell [μm] 0.7 1.4 3.4 7.1 15 2537 52 D_Coated_(—) 401 403 407 414 431 450 474 504 AGM [μm]

All documents cited in the Detailed Description of the Invention are, inrelevant part, incorporated herein by reference; the citation of anydocument is not to be construed as an admission that it is prior artwith respect to the present invention.

While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention. It is thereforeintended to cover in the appended claims all such changes andmodifications that are within the scope of this invention.

1. A water-swellable material, comprising water-swellable polymers thatare coated with a coating agent, which comprises an elastomeric materialthat is phase-separating, having at least a first phase with a firstglass transition temperature Tg₁ and a second phase with a second glasstransition temperature Tg₂,
 2. A water swellable material according toclaim 1 wherein the difference between Tg₁ and Tg₂ is at least 30° C. 3.A process for making a water-swellable material that comprises coatedwater-swellable polymer particles, said process comprising the steps of:a) obtaining water-swellable polymer particles; b) applying a coatingagent, wherein said coating agent of step b) comprises an elastomericphase-separating material that has at least a first phase with a firstglass transition temperature Tg₁ and a second phase with a second glasstransition temperature Tg₂, to at least a part of said water-swellablepolymer particles; and optionally the step of c) annealing the resultingcoated water-swellable polymer particles of step b), so as to obtainsaid water-swellable material.
 4. A process according to claim 3 whereinthe coating agent is applied subsequent to step (a).
 5. A processaccording to claim 3 wherein said coating agent is wet-extensible andhas a wet-elongation at break of at least 400% and a tensile stress atbreak in the wet state of at least 1 MPa.
 6. A process according toclaim 3, wherein the coating agent has, in the wet state, a wet secantelastic modulus at 400% (SM_(wet400%)) elongation of at least 0.5 MPa.7. A process according to claim 4, wherein the coating agent has, in thedry state, a dry secant modulus at 400% elongation (SM_(dry400%)) and awet secant modulus at 400% elongation (SM_(wet400%)), wherein the ratioof SM_(wet400%) to SM_(dry400%) is between 1.4:1.0 to 0.6:1.0.
 8. Aprocess according to claim 3, wherein said coating agent has a MoistureVapour Transmission Rate (MVTR) of at least 800 g/m²/day.
 9. Awater-swellable material comprising coated water-swellable polymerparticles produced according to the process of claim
 3. 10. A processaccording to claim 3 wherein said elastomeric phase-separating materialhas a Tg₁ of less than 20° C. and a Tg₂ of more than 50° C.
 11. A water-process according to process according to claim 3, wherein theelastomeric material is a block copolymeric material, having a molecularweight of at least 50 kDa.
 12. A process according to claim 11 whereinsaid coating agent comprises at least one block copolymer selected fromthe group consisting of polyurethane-co-polyethers,polyurethane-co-polyesters, polyurethane/urea-co-polyethers,polyurethane/urea-co-polyesters, polystyrene block copolymers and blendsthereof.
 13. A process according to claim 3 wherein at least a portionof said water-swellable polymer particle are individually coated by thecoating agent in the form of a continuous shell around, said shellhaving an average caliper of 1 μm to 50 μm.
 14. A water-swellablematerial of claim 11 wherein said shell is substantially uniform with aratio of smallest to largest caliper from 1:1 to 1:3.